Dear Carolyn:

I have been seeing the same guy for three years. He has made me feel really happy and great about myself, makes me laugh, and we have a very fulfilling relationship.

The one problem has been our trust issues, which we knew we would have. He had a history as a cheater, and I have a history as a cheat-ee. We have seemed to work most of them out, but over time I have always had my concerns.

This summer, he was unemployed, and I worked long hours. I felt something was wrong most of the summer ... and finally snooped, only to find out about a few lies he told, and a sketchy message from a girl. He admitted he made out with the girl at a bar this summer, and also admitted to several other lies he told recently about who he was hanging out with at bars, and his history with women I've met -- almost white lies, in order to "avoid conflict."

My first instinct was to break up with him, but he came forward with a robust plan I didn't expect -- and in a week he has gone to therapy, decided to not go out until I can trust him again, and to change his life even when I do trust him again so he is not ever in a risky situation. The biggest plan is to practice 100 percent honesty with me.

He says this change is not all about me; he feels he is ready to change himself whether I stay with him or not. He is 27. Am I wasting my time by giving him a second chance?

-- Wishing to see into the future

It's funny -- we tend to give people more credit for saying the wrong thing, because at least we're sure they mean it.

We celebrate hearing the right things -- therapy sought, responsibility taken, respect given, humility shown -- with skepticism verging on outright disbelief: "Great. What's the catch?"

It is, of course, a valid question, and if you decide to take him at his word, then you'll need to keep your mind open to any possible outcome, including one where you discover he manipulated you from beginning to end.

If that sounds more like living in suspense than being part of a trusting relationship, then think of it this way: No matter what he promises, no matter how plausible -- no matter what his history or yours, in fact -- the sensible approach remains the same. Live each day, be receptive to truth, make choices accordingly.

This is not to suggest that you scrutinize every detail of the past, present and future; that's just misery. Instead, my advice is to discard whatever narrative you're tempted to superimpose on yourself, your boyfriend, your relationship and whatever else, and just live by the reality you have in hand.

That means recognizing that your partner is a temptation-wrestler or birthday-forgetter or stress-eater or emotion-bottler or whatever other trait just isn't going away, no matter how much better life would be if it did.

And it means choosing to stay with someone ONLY if you can see these things as the price of a life that suits you well, not as temporary obstacles to some imaginary better life. Think cars: Either having one is worth the nuisance of insurance, gas, parking, repairs, etc., or it isn't, and you sell it.

With this guy: Cheating is a real possibility. Can you accept that when it happens? Enough to quell the nagging fear? "Not ever in a risky situation" (equal sign) delusion.

There's no greater obstacle to this kind of pragmatic thinking than the human taste for narrative. We see ourselves as This, or our relationships as That; we try to prove we're Someone or live down Something. You're doing it here. You've waited for him to prove whether he fits the cheater rule or the exception. Now it's, "Can he change?" -- and more waiting.

But people are too complicated for such reductive thinking, and applying it usually means you're overlooking other, important things.

Please accept that anyone can cheat on anyone -- and so what matters is whether you're in a relationship worth the risk things will go wrong in the ways foreseeable and otherwise: cheating, infirmity, unemployment, sick child, unforeseen conflict, whatever.

And please also look inward, to see why you keep assuming high risk despite a low tolerance for it. Where have you rationalized, or indulged bad habits, or ignored warnings? Where have you stuck to your narrative after the facts stopped supporting it?

I can hear the "Once a cheater, always a cheater" crowd screaming for me to shut up, and I'll grant, it's often that simple. But are you comfortable with fidelity as the variable that counts the most?

Email Carolyn at tellme(at)washpost.com, follow her on Facebook at www.facebook.com/carolyn.hax or chat with her online at noon Eastern time each Friday at www.washingtonpost.com.

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