What am I supposed to do about a horrible step dad?

Alright, I’m 16 years old, just got my license, just applied for a job at Subway. My mom and my dad got divorced when I was 3 years old. I didn’t understand until my mom started dating Mr. John. Before Mr. John, everything was so wonderful. I loved my mother so much, we were best friends. Then she started dating him… I was 7. He didn’t really talk to me until we moved in with him and his mom. Then everytime I came home, he’d tell me to show him my math how, and he tried to explain THE HARDEST WAYS how to do the problems. And me being only 7, I didn’t get them. He would yell and yell at me. This happened everday day. So every time my mom came home, I’d be crying. I had an asthma attack about 3 times because he made me cry so much. I tried running away from him because I didn’t want to hear him yell, but when I ran up the stairs he would always trip me. So this was every day life in that house. When I was 9 we moved to a town-house. He would yell at me for stupid things over there too, and I didn’t understand why. One night, we were eating dinner, and I spilled salt on the table. He just about flipped the table over. I don’t know why he got so mad when I could have just cleaned it up. My mom got really mad at him for being so stupid. And they got in a physical fight… I always think about it. He hit her and pushed her on the stairs and, just… I couldn’t stop crying. My mom told me to go in my room and lock the door. A few minutes later she came in my room with a phone and her keys and she called Mr. Johns friend, and he picked him up for a few nights. And then he proposed to her. I really HATED that she said yes. She knows how he treats me. A few nights before the wedding I told her that I really didn’t want her marryin that man. She told me it would get better, she promised. Here we go, 7 years later. I have a brother and sister now, 2 and 3. It’s worse than ever. Every day I come home, he has nothing positive to say to me. There’s always, ALWAYS something I do wrong according to him. And he can’t just talk to me about it, he has to yell no matter what. He can’t live through a day without yelling at me. He spits in my face when he’s yelling. He’s given me bruises on my arms from grasping me so tight and shaking me. Just EVERY LITTLE THING! It’s not even a big deal, but he has to make it a big deal. And he’s just so literal. Every time he’s yelling at me and I look away, he goes ‘Don’t turn your head like that!’ or “Don’t breahte like that” or “Don’t look at me like that!’. He thinks I’m being a smartass to him all the time, which I’m so not because I’m not that kind of person. I mean, I do stand up for myself, I tell him that he can’t talk to me the way he does because he’s not even my father. He says he is all the time, and he wonders why I don’t consider him my father. Why would I consider him a father if he treats me like this all the time? And when he punishes me he takes away the phone, my laptop, TV priveleges, turns off the lights in my room, and ‘locks’ me in my room; he opens my door and puts a baby gate up. How stupid, I’m 16 for cryin’ out loud! And what hurts the most, is that my mom lets him do this. She used to tell me that I was the love of her life. And she doens’t anymore… she just watches. What am I supposed to do? Am I the one that’s crazy? Please answer honestly. If you asked, I could probably explain things more in detail. Thank you.