My stepdad

My mother married my stepfather 6 years ago. Everything was fine for the first year. Then I saw his true colors. He would come home drunk or high on some drug. He'd try to beat my mom but I would hop in and fight him off. There was one night where it got so bad he had my mom pushed up against the wall and was choking her. Her face was turning blue and I had to protect her. So I ran at him and flipped him over the table. He got up and slammed me on the ground. At the point where I could get up I went to call the cops but my mom and stepdad came at me telling me not to call the cops but I did. And now everything he does is my fault. He gets in a crash? It's my fault. He drinks? My fault. He does drugs? My fault. Everything he does is my fault. He's done so many things and mom says she's gonna leave him but in the morning everything is fine. Like nothing ever happened. And I can't make it end because I've already tried and nothing ever works