Help.

I have been with this guy for almost 2 years now and I'm so confused. One second he wants to have a child with me then other times he tells me if I got pregnant he would punch me in the stomach. I'm only 17 and I know I shouldn't be worrying about this but I am. What if I get pregnant? Should I leave him? Should I stay with him? Just his thoughts make me paranoid for what he was saying. I just wanted some opinions.