You're right when you say that you don't want to hold stuff over each other's heads forever, because what's the point. But here's the thing. The stuff that got your M to where it was was UNINTENTIONAL. Obviously when we get married we don't INTEND for it to end in divorce, so the mistakes we make are just that - mistakes.
In my case, one of my mistakes was bottling up how I felt too much - I've always been somewhat of a private person, one who "holds his cards close to his chest." I didn't want to bother others with my problems, and figured I'd deal with them myself. I didn't realize that it was also shutting my W out and adding to our communication problems. BUT...she did plenty to contribute to the problems as well. The difference is that I've acknowledged my responsibility in it and am trying to work on those things. She really hasn't tried to do that at this point.
Now, here's the key thing. there are things that unintentionally bring about the demise of an M, over time. But an affair, is a CONSCIOUS CHOICE. In addition, choosing to give up on the marriage is a CONSCIOUS CHOICE. She hasn't given you a say in these things, although certainly they've affected or involve you. This releases you from certain obligations my friend. Treat her as the mother of your children and as any decent person would treat another, but she doesn't deserve much more than that, IMO.
My point is that I don't believe that something like, for instance, your anger and yelling was a CHOICE; it's simply who you were at that time. You identified that as something or someone you didn't want to be, and worked pretty successfully to change and improve that part of you.
But when it comes to things that are truly conscious choices, i.e. "I don't want to work on this marriage any more," it's not forgiveable, and as Cori said, it's not what friends, much less spouses, do to one another.
Don't hold anger towards her; that's something you don't deserve to do to yourself. But your true friendship is not something SHE deserves either.
"Our greatest glory is not in never falling but in rising every time we fall." -Confucius
"God alone decides the contest; but we must put our shoulders to the wheel." -Adm. D.G. Farragut
Kevin-38; XW-36 M-2.5, together 4 Bomb-1/6/07; D-6/27/07