You're absolutely NOT the asshole here. I had a shitty childhood and an abusive stepfather, although not nearly as bad as yours. Mine was only verbally abusive, and occasionally hit my mother, but never hit us kids. Just lots and lots of verbal abuse, drugs, constant tension and fighting between him and my mother, etc. He even hit his own mom closed-fist in the face once and knocked her to the ground, because she called him on his bullshit when he was raging drunk. But none of that holds a candle to what you've been through. And yet, it took me many years to come to terms with what I'd been through, and to let go of the anger and resentment, both against him and against my mom for continually choosing to keep him in our lives when it was clear that he was making our lives hell.

What your parents did is completely unconscionable. They should be utterly ashamed and groveling at your feet to forgive them. Granted, that's not a realistic expectation, but the point is that you are absolutely in the right here, and they are still refusing to own up to what they've done to you.