I think your feelings of hurt and betrayal are completely normal, and you’re going to have to just give yourself time to feel them as they come up and then let them pass. Eventually, it won’t sting as much, and it sounds like you realize you’re not losing a great friendship here, so once you get past these feelings of betrayal, you should feel much better and also won’t be friends with someone who would be involved with your husband… that was a huge betrayal in my book. A friend should NEVER do that, let alone a best friend.

Is it possible that part of you could also be mad at yourself for trying to forgive her and move on despite what you know she did, only to have her turn around and act like you are the one in the wrong? I had someone do something similar to me a few years ago (not involving cheating, but still betrayal) and when I dug deep, I realize part of my anger was coming from me feeling foolish at myself. I was mad at me, too.  If that’s the case for you, as well, again, it’s natural… it’s just something worth recognizing, feeling, and then forgiving yourself for trying to do what you felt was the right thing to do at the time, and letting it go.