That was such an emotional and sad story, very depressing.
I wouldn't know what to do, but some of the replies about this are worth trying.
All I can say is I understand what you're going through. I've had a terrible marriage with my cousin, though it finally ended in 2004, I still become sad and angry sometimes thinking about some of the things that had happened.
I have anger towards my parents. They wouldn't even let me divorce my cousin, so I ran away (to a womens shelter) with my children. My Dad even said he'd kill me when I ran away. I can't get over the anger I have when I think about everything my parents did and what my inlaws did and how the rest of the family made things worse. Your situation isn't exactly the same, but I too had to marry someone I didn't even like and I too wasn't allowed to refuse him. And listening to my parents gave me many problems too.
I noticed I even hate my parents, very often I still hate them. I know it's bad in Islam, but I can't seem to get over my hatred for them. For the sake of Islam, I did try to have a normal relationship with them, but I just can't. The anger, the sadness, the hatred even won't go away.
I'm afraid I can't advice about how to forgive your parents. I'm still struggling with that problem myself. I want to say something to make you feel better and help you to solve everything, but there isn't much I can say about this.
One of the things I've learnt from my problems is, that you have to talk about them. I couldn't talk about mine, I didn't want to think about the sad and some terrible things that had happened. So I didn't talk about my problems, I tried to live on as if nothing had happened to me.
Don't do that. It will eat you from inside. I did that. But that makes things worse. Years later the memories of what happened back then, still trouble me sometimes, because I had kept everything inside and tried to live on without any healing process. Try to find someone you can trust and who can understand you. Talking about it will help you to understand things better and to relax and maybe to let go a few issues. Insha Allah everything will be better for you.