He can do what most women do: INVENT a reason for dumping her.
Here's how one of your old letters goes:
"Each of the two women I dated in the past year ended our involvement early on with a big explosion about a little thing that couldn't have been the real issue. What is it about human nature that caused them to end a relationship by bringing up false issues? In both cases, the women could have just said "Look, this isn't going to work out, let's just end it." Maybe I have a pattern of picking up women who tend to dump this way..."
A.G.: You were probably a victim of Single Women In Search of Decorator Relationships...

I loved this one so much, I have it tacked over my computer.

"The right thing to do is to tell her you don't click as soon as you've figured that out."

Spot-on.

I wonder about this guy's personal details. He's probably in his 20s. But if he's eg. in his forties and divorced then it's worth taking time with someone who is hot, smart, and kind.

Could the LW take the old, "It's not you, it's me" approach? Seems to me that's what he's describing anyway.

"I think you're wonderful, and I don't regret the time we spent together, but I am sure in my heart that this is not 'it' for me."

"My heart is not in this, and it's unfair of me to keep it going. I don't have the feelings I should have by now."

"I don't want to pretend to feel things that I don't, because it's not fair to either of us."

I think all of the above are honest and unwavering, which is key in a breakup. There are no good counterarguments to be made.

I worry that ITY,IM can be an unkind approach. It generally implies that that the breaker-upper is breaking up because he's damaged in some way that makes him unsuitable for a relationship right now.

This can lead the ex either to 1) wait around for him while he works through it, or 2)feel hurt and humiliated when he manages to have a perfectly fine relationship with someone else next month.

It's not her fault, but she kinda IS the problem. She's not the girl he wants.

Before LW does anything permanent to a relationship with someone who is "smart, sweet, and kind," not to mention "faithful," he should go speak with a counselor to make sure that there aren't self-issues that are keeping him from attachment or commitment. It would be a shame to discover that after breaking up he's got some issue that could have been resolved with some therapy.

I think David is on to something. The LW has had two relationships with women who cheated on him. Now he's found one who's good to him and he's ready to break up. Hmmmm.

It's possible he is putting up a barrier. If the chemistry just isn't there, so be it, but it wouldn't hurt to make sure he isn't sabotaging himself.

Insufficient Poison: It's not her fault, but she kinda IS the problem. She's not the girl he wants.

Exactly. "It's not you, it's me" typically (although not always) means "it's you."

The three comments you proposed were very good.

honest and unwavering, which is key in a breakup. There are no good counterarguments to be made

Well said, IP. This applies to more than just breakups. A friend of mine went out with a guy she wasn't that interested in a few times because he kept asking her out at work (she was waiting tables). When she told me, I asked why she didn't just say no. She said "I did, I said I was busy", "not ready for a relationship", etc.

I told her excuses only give him something to argue against. Just say thank you, but no, and leave it at that.

It's OK, Crid. It might be hard to understand, but she just wasn't as "into you" as you are.

Things will get better.

Let's pretend you were breaking up with this girl because she has an annoying voice and weird teeth. It's not like you'd say that to her face--you'd use one or more of the "it's not you, it's me" lines that IP listed above. Most breakups sound pretty much the same--either because you're telling the truth, or because you're using a cliche to soften the blow. In this case, you happen to be telling the truth. So what you're really asking isn't "how do I explain this breakup to her?" but "how do I justify it to myself?"

Here's one way to think about it: there's 3 billion women in the world, say at least 50,000 eligible women in your age range within the nearest metropolitan area. There's no way ALL of them could possibly be right for you, but many of them are going to SEEM right for you--until you get to know each other well enough to say, nah, it's just not meant to be. That's how dating works. It's unavoidable.

And the kindest thing you can do when you realize that someone isn't "The One" is to let them go as soon as possible, so they can be free to meet someone else. That's much better than stringing someone along and allowing them to make plans around a relationship that isn't going to last, or manufacturing drama until one or both of you has an excuse to pull the plug. Do the mature thing and break up now, skip the dramatics, and part on good terms.

The more the direct the better. I think men should figure this out - blunt is painful and it makes a woman angry, and that anger is much more therapeutic than a condescending "apology". Wnen a guy seems really fearful of hurting a woman, it doesn't make him seem sensitive, just full of himself. And as for suggestions that he seek therapy in regard to a possible unconscious aversion to fidelity - by all means seek therapy, but leave the woman, and ergo, leave her out of it.