So, trying to come at this from a Christian perspective, the OP being a devout Christian (right? I'm new here, but I have that impression of the OP). Sorry if this is a wall of words ... I have a lot to say, I hope I don't make your eyes glaze over.......
First of all, Matthew 18:21-22, where Jesus tells Peter to forgive his brother 70 x 7 times. Go back and re-read that in context. The parable Jesus uses to exemplify this teaching is of a servant who is about to be sold into slavery along with his wife and children, in payment of a large debt. He begs for mercy and the master takes pity and forgives the whole debt. Then the servant turns around and demands payment of a much smaller debt from a fellow servant, who also begs for mercy but is denied it. When the master finds out, the first servant's punishment is worse than the original threat: "his master handed him over to the torturers until he should pay back the whole debt".
So throughout biblical history we can see that God threatens wrath against the people for their sinfulness, but relents either because of their own repentance or the intercession of a holy person. Either they beg for mercy or someone begs on their behalf. But even if He relents once, if the people continue to sin, He will ultimately punish them. But if your stepfather was unrepentant, you could not forgive him. What you loose on earth is loosed in heaven, and what you bind on earth is bound in heaven ... we Catholics apply that teaching to the sacrament of Reconciliation (confession and absolution). The sinner cannot be absolved if he's not repentant. He has to repent and ASK for forgiveness, and if he's not contrite in his heart, the priest can say "you're absolved" but he will still be bound to his guilt in heaven.
Again, there is the teaching about turning the other cheek: if your enemy strikes you on the cheek, turn and offer him also the other cheek. If he takes your coat, give him also your cloak. If he forces you to walk a mile, walk two miles with him. OK, this one's a little harder, given that Jesus Himself gave the ultimate example of peaceful submission to His enemies, allowing Himself to be crucified. But remember that Joseph & Mary fled into Egypt to protect Him from earlier enemies. Remember that He drove the money-changers out of the temple -- with a whip, according to John (John 2:15). He submitted to the crucifixion for a purpose, according to God's will. Just like Gandhi and King taught peaceful non-violence, submission to abuse can transform the abuser.
If there is no transformation in the situation, I think that your submission to an abuser like your stepfather, when you became able to oppose him, could have amounted to collusion with his sin. This is not advice to any other victim of domestic violence, since as others have pointed out, abusers are more likely to become MORE violent when they are directly opposed. But in your case you were able to successfully stand up to him, and I think you did the right thing. Sometimes sin has to be resisted in order for a transformation to occur. Anyway, you stood up to him without (I gather) doing him any serious or permanent harm. I used to see this all the time at work: women colluding in sexual harassment and discrimination by not calmly and assertively correcting the abuse at the very beginning. Those women who were confident and assertive professionals were treated with much more respect, in a very sexist environment.
OK, all that said. Holding onto anger and resentment and hatred hurts YOU. How to let go of it, especially if he is NOT repentant? One, now that you are out of his power, stay away, don't let him add to the abuse. Two, know that sin hurts the sinner most of all, and pray for his conversion. Three, keep doing what you did with this post, i.e. examining your role in the relationship and its effects on your character. For this, I highly recommend the book Codependent No More, I think the author's name is Melody Beattie. I also highly recommend Al-Anon or its offspring, ACA (Adult Children of Alcoholics).
sorry again for the wall-o-words......