Honestly. I'm sure there are times when you are alone where you cal make a phone call to the police.
Don't be scared.
Just do exactly what Wairuanor said.

What you should do is write a note to one of your teachers. Write down everything that he has been doing to you. Or you can tell the teacher that you need to talk to him or her outside the hallway. Because you have to get help. If you don't get help his going to end up killing you anyways. It's important that you get help now. What he's doing to you is very wrong. He probably has no idea how much he's hurting you. My father was an alcoholic. He also abused my mother. And it's tough. Ofcourse he went to prison. And once he got out my mother gave him another chance. And soon he did the same sh*t over and over again. He went to prison once again. Right now my parents are divorced. Be brave and talk to one of your teachers...

tell someone. He may threaten you but having an abusive bf is not right. He should serve some consequences. Tell someone that you can trust. And make sure your bf is not around.