Bmom has some solid words.
Affairs are an insidious thing and very complicated. Coupled with the fact that it nearly impossible to separate emotion from sex -- even if you *think* you can going in.
Here's the cold, hard truth -- she's hardly a whore/slut as many of you judge her to be. She probably loved the other guy. That's right, loved. It started as a friendship and progressed from there. He was meeting needs that she needed met. And having her needs met felt good, so the relationship continued.
It's not his fault by any means. Cheating is a symptom of a larger problem though.
That said, she loved her husband more. And her husband was ultimately able to meet more of her needs than the other guy. She loved him enough to end the affair on her own, which is a very difficult thing to do (it's like breaking off a normal love relationship), and to be straight honest when he asked her about it. Honesty is not the hallmark of a whore. Neither is being a decent mother.
The last 2 years have been great he said. That's what's real. You guys think he should ruin his life, his wife's life and his kid's life over some shit that happened 2 years ago that's been (mostly) dealt with?
Here's some more cold, hard truth -- he divorces her, he'll probably lose his kids. That's right, she cheats, wrecks his world AND he loses his kids. It doesn't matter that she cheated to the courts. Unless he can prove incompetency as a mother (which is also pretty damaging to the kids if it's false), the kids are hers and he becomes an every-other-weekend daddy. Unless you have your own kids, you have no fucking clue what this means to a dedicated father. So don't speak.
And before you go on about it's better for the kids to live with one or the other as long as the parents are happy, go to divorcebusters and read the studies they cite that show that unless there is physical violence in a relationship, the kids are still better off -- even if the parents don't like eachother. But that's not even the case here -- the last 2 years have been great, he loves her, she loves him. She fucked up. Bigtime. She was selfish, manipulative, out-of-her-mind ... But you know what? 99% of all people would fuck up to under just the right set of circumstances.