sperm donor (and not the good kind)

I had my daughter 4 years ago and her sperm donor denied that she was his after kicking me out at 3 months pregnant. We got a paturnity test and she was 99.9999% his (which I knew). He seen her once we went to friend of the court when she was 4 months even then it was only once a month maybe until she was 6months. His mother stayed in her life for a bit longer up until last year. I found out he was going to her house to see my daughter. Since he hadn't seen her at 6months old he married my then best friend, signed off his rights to my daughter, had a daughter of his own. He apologized for what happened between us and I for gave him for that. But I can't seem to forgive him for forgetting about my daughter (she has an amazing dad now my husband he's been there since I was 4 months pregnant and even adopted her) Maybe I do need to just let it go but I don't know how. Any advice?