I'm sorry :(
Therapy will likely help. Something that resonated for me in the past was when someone said about her terrible parents, "I had to grieve the parents I deserved but didn't have."
Grief is exactly what I felt. Grief for the father I wanted and didn't get. Sorrow for the kid I was, who watched silently as my father abused my mother, my sister, everyone. Sorrow for the people I loved, who he hurt so much. Also grief for him, because he was my father. I mourned him for a year.
But throughout it all, I stayed resolute. It probably helped that he wasn't in the same city and he didn't care too much.
A couple of years after I cut him off, he sent me a thick letter. I knew from my sister - who was forbidden to talk about him but nonetheless quickly squeezed in an appeal on his behalf (she was ever his emotional laborer) - he wanted rapprochement.
I thought about reading the letter, opening the door again, for several weeks. I was 40, not a confused kid or hopeful 20 year old anymore. I knew what he was like, I knew he was not capable of change. And how he had treated people had been heinous. Truly unforgiveable. On reviewing everything, I knew that I could not have someone like that in my life or my family's life.
One night, I walked the whole night through my sleeping city with the dog. At dawn, when the sun was rising and the magpies began to warble, I returned home, retrieved the unread letter, burned it, and spread the ashes in the river nearby.
I had already stopped grieving a while earlier, but that little ceremony allowed me to let go of all the residual anger. I felt at peace.
I have never regretted any of this. I look back over my life and see so clearly how that incredibly difficult and painful decision I took 20 years ago spared not just myself but also my innocent children from the knife-laden thresher machine that was my father.
OP, I hope one day you will find peace too.