I started seeing a guy whose previous relationship ended because he cheated. He insists he really learned his lesson and would never do it again. Should I trust him, or should I go by that line, "once a cheater, always a cheater"?

--Worried

People in relationships do develop little traditions -- like coming home every night and checking the closet for their boyfriend's sex partners.

The question is, does the skeleton that your boyfriend's yanked out of the closet point to a heavily populated closet in your collective future? This is ultimately a question of whether he's a cheater -- a person psychologically "wired" to be prone to cheating -- or a person who once cheated. There is a distinction. Sometimes, somebody cheats just to see what it's like to walk on the bad boy/bad girl side -- the (heh) Socio Path. And sometimes, in the moment (SEXXXXX!), somebody who's generally considerate puts their partner's feelings on "ignore."

However, evolutionary psychologists David Buss and Todd Shackelford found there seems to be a cheater personality -- a trio of personality traits common to people prone to infidelity: narcissism, low conscientiousness, and "psychoticism."

That last one -- psychoticism -- suggests an ax-killing hobby, but it's actually researcher-ese for a combination of impulsivity, unreliability, and an inability to delay gratification. Narcissism, of course, is the "Me! Me! Me!" personality trait, reflected in self-absorption, self-importance, exploitativeness, and an empty well in the empathy department. Low conscientiousness is the personality trait of the inconsiderate, reflecting disorganization, poor impulse control, and an inability to delay gratification.

Yet another factor is a personality trait that psychologist Marvin Zuckerman named "sensation-seeking." People "high in sensation seeking" crave a variety of new, complex, and intense sensations and experiences and will take physical and social risks to get them.

Talk is cheap -- especially for the ethically sketchy, the morally underfunded. Look at the guy's behavior and thinking -- in your brief past and in the weeks and months to come. See whether it adds up to good character or reflects the cheater personality markers. Sometimes cheaters change, but personality traits have a substantial genetic component, so cheaters mostly just change who they're cheating with. If your boyfriend's moral compass is secretly set on Booty Call North, you're setting yourself up for many joyful years of checking his shirts for some hussy's self tanner and trying really hard to believe that he only goes to strip clubs for the music.

For pages and pages of "science-help" from me, buy my latest book, "Unf*ckology: A Field Guide to Living with Guts and Confidence." It lays out the PROCESS of transforming to live w/confidence.

My fiancee and I mutually ended it several months ago, but she's staying in touch, reaching out, texting, etc. It's really hard to move on when she's trying to maintain a connection. I've hinted at this, and I know she isn't interested in rekindling romantically, but nothing changes.

--Disturbed

My late Yorkie, Lucy, now resides in a tiny urn in my living room; I didn't have her taxidermied and mounted on an old roller skate so I could take her on walks like nothing's changed.

After a breakup, it's hard to go your separate ways if you never stop being together. Though your situation sounds like "Brokeback Mountain" for straight people ("Bro, it's super hard to quit ya!"), there might be something else keeping your ex-fiancee around.

Ancestral humans became a cooperative species, living and working together in groups, leading to a need to identify (and avoid) the takers among the givers. We seem to have evolved to act in ways that elevate our reputation, which is basically a social credit check for the sort of people we are. For example, evolutionary psychologist Bo Winegard and his colleagues theorize that reputation promotion is one of the evolutionary functions of grief. They see the expression of grief as a form of advertising for our character, showing us to be loyal and committed allies who "form devoted bonds" with people in our lives.

This zombie fiancee thing -- the ex-fiancee who keeps coming back and eating your well-being -- may be your ex's way (probably subconscious) of promoting herself as a good friend, a caring person who doesn't just shut the door on somebody she's romantically done with. This could help her seem more attractive to the next guy -- which is surely help you aren't interested in providing, especially at the expense of your need to heal.

Toss the hinting. Tell your ex-fiancee that this maintaining-a-friendship business does not work for you, and ask her to stop contacting you for now and/or until you let her know otherwise. Cutting off contact will help you get used to the new normal -- you and your former fiancee walking off into the sunset apart, in totally different directions...at least until your new wife is in the delivery room, giving birth to your first child. A familiar voice behind you: "Guess who's here to finally cut the cord!"

For pages and pages of "science-help" from me, buy my latest book, "Unf*ckology: A Field Guide to Living with Guts and Confidence." It lays out the PROCESS of transforming to live w/confidence.

My 22-year-old son's new girlfriend is extremely pretty. She has a great figure and dresses to show it off, so I understand the attraction. However, she's also spoiled, lazy, and kind of a scam artist. (She bragged about cheating a small business.) I pointed out her shortcomings to my son, but he refused to listen and even defended her. Can I get him to end it without being the overbearing mother?

--Upset Mom

Though you see only flaws, your son sees a lot in this woman: BOOOOOOOBS!

It's natural you'd want to scold him away from a train wreck with cleavage, same as you'd save him from a speeding car about to turn him into a human hood ornament. However, telling him all the reasons this woman's awful -- which amounts to pressuring him to dump her -- is exactly the wrong thing to do. Consider Romeo and Juliet (and let's momentarily forget they were fictional characters). As teen love goes, I suspect they would've gotten bored and cheated on each other in under a month if their parents hadn't been all, "We forbid you to see that Montague knave/that Capulet tramp!"

When our freedom of choice -- our freedom to do as we want -- is threatened (even just by people trying to persuade us to change our ways), it triggers a motivational state that social psychologist Jack Brehm called "reactance." Reactance is a form of rebellion -- a "reaction" against control, energizing a person to resist, to keep engaging in the behavior they're being pressed to stop. Reactance can even strengthen the person's resolve -- increase their desire for whatever (or whomever) somebody's urging them to part company with. Basically, by telling your son all the reasons he should dump this woman, you turn him into the pro bono defense attorney for her humanitarianism -- like how she, um...um...runs a rescue for designer handbags!

Character doesn't always seem important in a partner until a person gets knocked around by somebody with some big vacancies in that department. In other words, if you want your son to dump this ethically elastic chickie, the ideal thing to say is nothing. Let him marinate in her bad character. Hard as it will be to keep mum, you might try to view him as midway through the natural recovery process in the wake of contracting a nasty parasite -- one that's 5-foot-7 and blonde with window-sized Gucci sunglasses you suspect she lifted from some distracted wealthy lady's restaurant table.

For pages and pages of "science-help" from me, buy my latest book, "Unf*ckology: A Field Guide to Living with Guts and Confidence." It lays out the PROCESS of transforming to live w/confidence.

My boyfriend is best friends with another girl. He told me they tried dating years ago, but nothing came of it, and they really are just friends. She's been very welcoming to me, but I'm still uneasy that he's so close with a woman he once dated. I can't help but wonder whether the bit about straight men not being able to be friends with women is true.

--Nervous

Picture the city dump. Sexually, to your boyfriend, this woman might as well be an old tire, a single dingy couch cushion (whereabouts of rest of dingy couch unknown), or a phone book from Buttcrack, Montana, circa 1982.

In fact, there's a chance he was never very attracted to her. Generally speaking, men are a lot less likely than women to turn down a possibility for having sex. Also, before he got naked with her, the prospect of having sex with her was what neuroscience researchers call a "novel reward" -- a term for feelgood stuff we have yet to experience. Excitement over the new might even be mistaken for the excitement of really being attracted to somebody, because novelty causes a surge in dopamine, the neurochemical that energizes us to pursue new and rewarding things.

The problem is "reward prediction errors," neuroscientist Wolfram Schultz's term for the difference between how great we think a new thing will be and how kinda-sorta okay it ends up being. When reality falls short of our expectations -- when somebody turns out to be sexy like used gruel -- dopamine goes into sag mode. This is effectively a neurochemical energy embargo -- a crash diet on the motivation juice needed to drive any further pursuit of whatever we found bummerific.

You might find it reassuring to ask your boyfriend why it didn't work between them and pry a little bit into how attracted he was to her. This could tell you that you have something to worry about, but at least you'd know. Sure, straight men and women can have trouble remaining just friends if they have any sort of hots for each other. However, a straight man who is sexually bored with a woman is one you can probably trust just fine to be in her presence. Even if she's naked, with head-to-toe body glitter, performing the (Lap) Dance of the Seven Veils.

For pages and pages of "science-help" from me, buy my latest book, "Unf*ckology: A Field Guide to Living with Guts and Confidence." It lays out the PROCESS of transforming to live w/confidence.

I've been dating this guy for a month. Things with him are really average. However, we met through a mutual guy friend, and I'm actually really into that guy. Could my staying with the guy I'm seeing spark jealousy in the friend and lead him to make a play for me?

Sext your boyfriend and ask him to forward it to his friend.

Kidding, obviously. But at least that would end things between you. That's the right thing to do -- as opposed to staying with the guy and using his interest in you as bait to attract the dude you really want.

By the way, it's probably unrealistic to think the other dude will swoop in, elbow his buddy out of the way, and run off with you. Mate poaching -- somebody "stealing" another person's romantic partner mid-relationship -- has likely been a common form of mate acquisition throughout human evolutionary history, explains evolutionary psychologist David Schmitt. However, it has its costs. Schmitt notes that mate poaching can lead to undesirable "social consequences": violent retribution from the poached person's partner, damage to one's reputation (especially for a guy who poaches his buddy's girl), and exile from one's social world.

The relationships formed through mate poaching also tend to be less than dreamy. Research by social psychologist Joshua Foster and his colleagues found that "individuals who were poached by their current romantic partners were less committed, less satisfied, and less invested in their relationships" than non-poached relationship partners. The sort of people who let themselves be poached (from their previous relationship into their current one) tended to have a wandering eye -- paying "more attention to romantic alternatives" and cheating more often than the non-poached.

The moment you realize you've got the lukewarms for a guy is the moment you should break it off and move on. You'll be that much further along in meeting somebody who might be right for you. Plus, your sharing any more than a date or two (and a chaste kiss, no nudity) with a guy you're not that into is likely to make his dude friends classify you as off-limits. Of course, it's also seriously unfair to the meh man (who is also a person with feelings) for you to slow-walk him off the plank. Sure, there's this idea that a romantic partner will be your shelter, but that's not supposed to mean they're the bus stop where you wait till the guy you're actually into picks you up.

For pages and pages of "science-help" from me, buy my latest book, "Unf*ckology: A Field Guide to Living with Guts and Confidence." It lays out the PROCESS of transforming to live w/confidence.

I'm a 36-year-old woman. I've had my share of men who shy away from commitment, so it's a bit of a surprise that the guy I've been seeing for a few months really wants to settle down. He's already talking about kids. While I really like him a lot, I worry that his rush to settle down is a red flag.

--Uneasy

When a guy yells something out in bed, it's a little disturbing if it's, "You make me want to put up wallpaper in a house in the suburbs!"

It's possible the guy suddenly had enough of the Tinder rando-lympics and began longing for a lasting bond with a woman. Clinical psychologist Judith Sills believes feeling this way causes a shift in one's approach to dating. The push to find the perfect "right person" gets cast aside for finding a right enough person at the right time. What makes it the right time is "readiness," which Sills calls "an internal process that acts as a psychological catalyst for commitment." This is readiness for true partnership -- for intimacy (and the vulnerability it requires). It "does not mean being without anxiety or ambivalence," Sills explains. But "readiness is a state of mind, an attitude of approach that helps you to push past the barriers created by these feelings."

Whatever the reason for the guy's rush to put up picket fencing, it's important to take things slowly. (You might give it a year or more before you make any big moves together.) Research by psychologist Michael I. Norton and his colleagues suggests that the more budding romantic partners learn about each other, the more they see dissimilarities -- clashes between them -- and the less satisfied they can become with each other and the relationship.

Do something people newly in love (or at least newly in hots) typically don't do: Seek out the clashes between you -- all the areas in which you glaringly don't want the same things, have habits that grate on each other, etc. If that stuff isn't enough to break you up, tell him you two might have a reasonable chance of going the distance together -- though not if he keeps talking to your womb on dates: "I'd like you to give me a male heir. How's Friday?"

For pages and pages of "science-help" from me, buy my latest book, "Unf*ckology: A Field Guide to Living with Guts and Confidence." It lays out the PROCESS of transforming to live w/confidence.

At family gatherings, my sister-in-law makes critical remarks about my appearance, like my shirt's very low-cut or I might want to lose weight before wearing the dress I have on. She only does this in front of others, and she says she just tells me because she cares about me. It doesn't feel that way. I'd really like her to stop.

--Feeling Attacked

When you're female, junior high never ends. The Hello Kitty knife in your back just gets upgraded to one by Cuisinart.

Women are said to be the "gentler sex," because we rarely see one drag another out of the bar by her ponytail for a parking lot beatdown. But women aren't better people than men. Female-on-female aggression just plays out differently -- less visibly, less identifiably -- than the male-on-male kind.

Psychologist Anne Campbell explains that women evolved to avoid direct confrontation -- physical fights or calling somebody out to their face -- and instead compete with other women through sneaky "indirect aggression." This is aggression that doesn't quite read as aggression, like the public shaming that wears the plastic nose and glasses of concern.

Another popular form of woman-on-woman sneaky sabotage is spreading mean gossip to knock another woman down the social ladder and maybe even get her ostracized. There's also "constructive criticism" -- supposedly well-intentioned remarks meant to stress a woman out, make her feel bad about herself, and get her to dim her shine.

Campbell believes women's tendency to use indirect aggression is "a result of their higher parental investment" -- the fact that they're the home and ground transportation for the developing fetus and are children's primary caretakers. A physical fight (or more male-style fighting words that led to a punchout-fest) could damage a woman's reproductive parts or kill her, and an ancestral woman's survival was key to her children's survival and to her passing on her genes.

People like you, who are repeatedly victimized by another person, often don't realize they never set any boundaries, never told the abuser to stop. This effectively sends their tormentor a message: "OPEN SEASON ON ME FOREVER! Keep doin' what you're doin'!"

Whenever your sister-in-law turns a family gathering into a forum on your weight or outfit, calmly assert yourself, saying only these words: "No more comments on my appearance, please." Be prepared for her to insist you're crazy, oversensitive, and unfairly accusing her. This is bait. Do not take it. Getting into any sort of debate allows her to cast you as neurotic and mean and cast herself as the victim.

Be prepared for her to "forget" and attack you again. Simply reiterate your mantra, in a cool, calm voice: "No more comments on my appearance, please." You'll shut her up without looking like the bad guy, but you'll both know what you really mean: "Inside me, there's a skinny person longing to get out, shove a Tide Pod and load of socks in your mouth, and put your head on spin."

For pages and pages of "science-help" from me, buy my latest book, "Unf*ckology: A Field Guide to Living with Guts and Confidence." It lays out the PROCESS of transforming to live w/confidence.

My boyfriend and I recently discussed having children. I want them, but he's a little on the fence. He says he needs to be in a better financial place before thinking about kids. I wonder whether that's just an excuse to put off the topic indefinitely.

--Worried

Children bring their parents a lot of joy -- and it helps to remember that as you're jazzwalking to the office so you can put your gas money toward your kid's fourth round of dental work.

Children are seriously expensive, so maybe your boyfriend just feels a serious sense of responsibility to support the little buggers while being unsure of exactly how many million bajillions that could take. Economist Daniel Ellsberg observed that we humans are deeply disturbed by ambiguity -- a lack of information about how things could turn out. Some people are so ambiguity-averse (aka uncertainty-averse) they'll opt for an immediate sure loss over the possibility of a future gain. It's why people sometimes sabotage a new relationship: They can't stand not knowing whether the thing'll tank, so they blow it up themselves.

To figure out where your boyfriend really stands, replace the ambiguity with information. Together, add up the costs of having kids (factoring in health care, emergencies, grad school, rehab, etc.). From that, project the date of his financial readiness. You might also ask him about any fears he has about having kids. Discussing them might shrink them -- or make it clear that he isn't daddy material and that you should start looking for a man who is. Though retailers allow you to return many items, even if they're slightly used, maternity wards don't work like that: "Excuse me, Nurse...these three kids turned out to be unexpectedly loud, sticky, and expensive, but I don't see your return policy on the receipts."

"Sir, those are birth certificates."

For pages and pages of "science-help" from me, buy my latest book, "Unf*ckology: A Field Guide to Living with Guts and Confidence." It lays out the PROCESS of transforming to live w/confidence.