My stepdad is being really mean to my boyfriend! What do I do?

I mean I already hate him! But now he's always mean to my boyfriend and for no reason. I mean yes I did spend the night at house one night but it was all his fault for arguing with my mom in the middle of the night and that's really emotionally painful for me to hear! Today my boyfriend was over our house and in my room with me when we were home alone, something my mom has never had a problem with because she totally trusts me, but he came in and started yelling at him and told him to leave and threatened him again, which is something he loves to do to him ever since the other night. When I confronted him he said I better be glad he doesn't forbid me from seeing him all together as if that's his right! Plus about an hour ago when I was on my cell phone with him he rudely took it away from me and hung up saying I shouldn't be on the phone with some guy this time of night (it's only like 11:40 though), when I complain to my mom she always takes his side! I don't get why he's always so mean to my boyfriend when he hasn't done anything wrong. How do I get him to stop being such a jerk?