I've also changed my name for this discussion.
I had an affair. It did not end well (and yet did not disturb my marriage, luckily) by I don't regret having had it.
My husband and I have had a less than good sex life for as long as I've known him, because my husband isn't very interested in sex. He promised over the years that things would improve and that his low sex drive was temporary (due to exhaustion from work, or this excuse or that excuse), so I married him despite my serious reservations about the sex. Of course it was naive of me to believe things would improve. Still, he is such a good husband, father and person in every other capacity, that I don't believe I made a mistake in marrying him.
That said, over the years I have begun to feel resentful over his sexual problems, whatever they are exactly, presumably a low drive. We have sex exceedingly infrequently, and it's a wonder I became pregnant twice. Even though I'm told I'm attractive, I began to feel hideous, then angry, and then depressed. After several tearful conversations last year, my husband gave me permission to sleep with other men, so long as I never told him about it. He said it would hurt him profoundly if I did (hence his not wanting to hear about it), but that he was much more worried about the possibility that I might leave him.
At around the time of this conversation, I found myself very attracted to my language professor (I'm trying to learn my husband's first language). Those months that led up to our eventual affair were some of the happiest in my life, so I can understand how difficult it feels to even think about ending things, Sanb. The man I had the affair with is also married--2 children. He'd never had an affair either. He led me to believe that he was falling in love with me, yet the second we 'consummated' our affair, he became strange and distant. He told me he felt nothing for me but lust and low-key friendly feelings, and that our relationship was never going to progress to anything more intense, and that he would never leave his wife and children, so it was imperative we keep our affair secret.
So I, too, tried to get into his mindset of separating the physical from the emotional. I thought I could do it, and carried on with the affair, finding it relatively easy to keep it from my husband. (Mostly I had to stop myself from talking about him all the time because that would have raised suspicions. And certainly we never rang each other, and emailed only occasionally.) Finally I had to face facts that I really was in love with this man, and yet he felt basically nothing for me. So I ended things because it was all too heart-wrenching. I'd gone off my husband, and was instead in a horrible unrequieted love situation. The other man was completely nonplussed when I ended things--he really didn't mind one way or the other, and that was hard too.
I think affairs have to end badly almost by definition. I'll probably be tarred and feathered for saying this, but I don't think having an affair is entirely or always a bad thing even though affairs do usually end up badly. For me, that intensity, while it lasted, was worth it. I would have an affair again, but then again I have an unusual situation with my husband and perhaps have less to lose than a lot of other people have.
I feel fortunate that I didn't do something stupid like leave my husband over this man. With some distance and objectivity, I see that I'm married to the better man by far.
Apologies for the long post. This is a difficult thing to discuss with friends. I'm glad I had an opportunity to talk about it.