I've had kind of the same thoughts on the "contributing situations" thing. You have an affiar, it's your fault. If I don't do enough laundry or listen closely when you talk about your friends, that's irrelevant, it doesn't justify it. Cheaters (and their sympathizers) will try to argue differently but it's mostly just blame-spreading if you ask me. Now if they were having enough problems to be separated or something, that could be a different story.

Anyway, if you want my read on this guy, I'm going to guess that when the affair was revealed, he went straight to forgive-and-forget without really addressing his own hurt feelings. (The letter writer tellingly doesn't say he was angry or gave her "holy hell" before forgiving her.) Now that she thinks it has blown over, he is resentful because he never gave himself time to grieve about it and he can't move on, and he is getting it out by picking a fight about her ex-boss.

This just goes to show if you're like me, you have to do something at that time (right after you find out). Don't be too quick to forgive-and-forget, nor instantly break up. But move out for a while, DO something that shows that there are serious ramifications. It has to be something that isn't pleasant at all for the cheater. Probably if infidelity happened to me again, I would just move out and get an apartment for a while, then see how I felt about it after that.