I haven't been in your exact situation, but I have been cheated on by a long-term boyfriend. We had been dating for over five years when I found out he had been seeing another girl for the past seven months. When I confronted him, he went crazy and tried to OD. It was awful. I only cried once through the whole thing though...when I saw a counselor for one session. I was really surprised by this because I am definitely a crier.
I did have the opportunity to really go off on him a couple months after the whole thing happened, which was the last time I saw him back in 2004. That probably helped. You boyfriend has missed his chance to do that (if he never did it), so I would recommend going to see a counselor. Solo sessions and then some with you would probably be the most effective.
Please be assured that your boyfriend is not upset that his marriage ended, he's pissed that someone would blantantly hurt him like this. His ex-wife did something that she knew would break his heart and she did it anyway. I still hate my ex, but I'm very happy our relationship ended and I would never want him back in my life in any way. But the fact that someone out there cared for me so little that they would do something to really hurt me is very upsetting.
I don't know if this all makes sense, but hopefully I can offer you a little comfort and advice. Hang in there!