As for your friend, you are saying that he second guessed his feelings, and "managed to plunge himself into a depression." Having been there - bad marriage, then a cheating spouse whose actions finally pushed me to divorce him, I can assure you that in spite of the GREAT relief one can feel from finally leaving a bad marriage, the fact that your spouse committed adultery is still incredibly painful. I would say that his depression was a perfectly normal response to a very sad situation. He didn't do it to himself - his cheating wife is who is responsible for his grief.
I think you're second guessing his feelings, Kathryn. You're assuming he's like you.