Complicated feelings

When my parents were together, my dad was an a-hole to my mom. I witnessed it, and he wasn't shy about doing it in front of me (I was 12 at the time). I think one of the things he did that stuck with me most, was him mocking her. Yesterday, I found out more about what he did to my mom when I wasn't present.

When my mom requested child support, his response was, "Sue me." He can't hold a job and he's mentally unstable; if I were to go into more details, you would agree.

I try my best to keep him out of my life, but when I am around him, he's nice to me, and I get trapped by his fakeness. I have to tell myself that it's just an act. Part of me feels I should be grateful for him because I wouldn't be here if it weren't for him. But he's a bad person, and I've learned there's nothing I can do about it. I seriously wonder if this plays a role in why I have anxiety