dealing with shame

I've come through the ex cheating on me and walking out on our children and me knowing it was not my fault and being able to hold my head up. I've told countless people the story, and while I've been emotional about it, I've never felt shame for it.

But recently I've hit a stage where I realized I'm ashamed that I picked who I did to be the father of my children. I'm ashamed that I married this man. I'm ashamed that I wasted 26 years of my life with him, and didn't, wouldn't see him for who he really is.

For now though, the shame I feel is manifesting in anger, and that's not a good thing. I feel as if I've taken a leap backwards in some ways, and I'm not liking that. I can offer myself a million reasons why I shouldn't be ashamed, but they all feel like excuses and justifications to me. 

I'm not sure what to do with this. I'm not big on the whole forgiveness
thing. I don't necessarily think it's something that has to be done.
Accept, yes. Forgive, not always. So is this something about myself I
just have to accept, or do I need to forgive myself for it? Certainly, I
need to learn from it. I'm not quite sure what the lesson is yet, but I
know there's at least one in there somewhere. There always is.