I also struggle with forgiveness. I often battle with replaying old sins I have committed in my head over and over. I then wonder why God chose to forgive me and why even let it happen in the first place. So I completely understand where you are coming from. The best suggestions I have to give you is first all
forgive him as Christ has forgiven you. I know it is easier said then done, but it is only hurting and dragging you down more to keep this resistment in your heart. I know as humans that complete forgiveness and coming to a point of being pretty well okay with the situation may take time and prayer. Second, I wasn't there but I image you probably gave it your all to make the marriage work out, but unless he was giving an effort to make it work too then it was just exhausting you to keep fighting in a situation that he had alright made up his mind on. Stop blaming yourself because it sounds like to me that if he didn't give you a reason for wanting to divorce in hopes that yall could work on it. Then I don't think he really wanted anything fixed. I hope this has helped and not come across as harsh. I pray for you and God bless you.
Philippians 4:13
I can do all things through Christ who strengthens me.