I feel for him and his family. It is never worth the cost but some good things can come out of such things if he and his wife can work through this. When my wife and I were having problems I asked for a divorce before ever considering consummating a relationship with the other woman. I think that is only fair and right thing to do. It turned out for the better. We worked things out without the baggage of that added betrayal for which I am thankful.
Yes the long term relationship syndrome, hard to separate true feelings there especially for a Man we have another set of thought process going on at the same time.