Abusive relationship

I have been together with my boyfriend for almost 4 years and we have a son who’s six weeks old. We have been living together for almost three months and have recently gotten into horrible fights at the point where I’m begging him to leave me alone and telling him I don’t want to be with him any more, but he never lets me leave, things get to the point where he’s pushed up against me yelling at me and I’m pushing him trying to leave but he blocks the door, hides car keys, takes my phone away until things calm down. I know I shouldn’t be with him but I don’t know why it is so hard to leave a relationship. I’m trying the hardest to not fight so my son can have a normal family but I hating being with him, yet I can’t build the courage to leave him. My mom has started to wondering if things are okay but no one knows about these horrible fights. I really need some advice.. please no judgement. I used to think girls were so dumb so staying in abusive relationships until I got into one. Things are always easier said than done