Hi Fluffy
Betrayal is a huge thing to deal with! I'm glad that you found this website as well, and glad that you don't feel so alone anymore. There doesn't seem to be much pain or frustration expressed here that someone else doesn't relate to -- sad, but reassuring to know that there are other people who struggle at times as well.
For me, the huge anger for the betrayal itself was one thing, but then the deep resentment that the betrayer seemed to be getting off scot-free while I'm left in pain and anguish to pick up the pieces created even more anger, focussed and unfocussed, at the unfairness of the world. Then I would get angry with myself for not being able to just let go of it -- forgive and forget, get on with my life -- as easily as the people around me seem to think I should.
There's a theory that depression can result from repressed anger, so I've been trying to figure out constructive ways to release my anger. Talking helps a little; screaming into a pillow helps somewhat; beating up a punching bag helps a lot. I know that taking it up with him isn't going to help at all because what I really want is for him to say he's sorry, show remorse, ask for my forgiveness, and, realistically, that's just not going to happen.
I suppose it comes down to keeping in mind that we can't change other people's behaviour, only our own responses to it. Allow yourself to be angry -- you have every right to be so regardless of what your friends and family might say -- and find a way that works for you to get that anger out of you. When you do that, you take back the power you're giving him to hurt you and cause you more pain. If you don't get the anger out, it will seep out anyway and in ways that may not be very positive or constructive.
I go to a self-help group as well, and I get a great deal out of the sharing of experiences, empathy and wisdom. I think you're doing the right things to get yourself through this -- just give yourself the time to heal as well.