Punched myself in the face

When I was a kid my stepdad used to threaten to “beat you within an inch of your life.” He would spank me but the beatings never actually went beyond that, though the threat of escalation never stopped. I moved out after highschool but nearly a decade later I had to move back in with him and my mom. I try so hard to stay on his good side but he’ll still flip out of nowhere and become very hostile and cruel out of nowhere and when he gets that way I just wish he would fucking do what he always promised to do instead of these mind games where he can pretend I’m the problem. He never acts the way he does when we’re alone if my siblings or mom are around. Maybe two months ago I thought we were ok but then he started being cruel again and it was so frustrating and when it was over I went to my room and for the first time ever I physically self harmed. I punched my self in the face as hard as I could but it wasn’t enough. So I kept doing it over and over. My face got swollen but the bruises stayed light. No one noticed anything was wrong. We haven’t really spoken since then and I isolate in my room and rot away. I work in the middle of the night so no one thinks it’s odd that I haven’t really left my room in such a long time. When I try to talk to him he walks away pretending not to hear me. I wish I could leave but I can’t afford it. I’ve always struggled with suicidal ideation but now physically punishing myself seems like the easier thing to do. Whenever I feel crushed by depression I keep feeling the urge to beat the shit out of myself and it’s scary. It feels real now that I’ve done it before. I don’t know what to do.