What do you do when your Boyfriend wont man up, and be a man?

i'm 18 years old. i know young, but i'm also about 20 weeks pregnant with my boyfriends child. Granted, he is doing alot to work with me when it comes to having the baby. About as much as his maturity level will allow, so to speak. But we're buying a house, and yet, he wants to let his single bachelor, drinking buddy live with us to help pay rent. He goes out every weekend to get drunk with his buddys rather than spend time with me, becuz the way he looks at it ';he only has so many months until he cant go out nemore...'; so he has to ';get it out of his system'; w.e thats suppose to mean. He makes up things hes doing when i know hes really smoking weed or drinking, and i cant count on him to just GROW UP when the baby comes, becuz if he doesnt i will be devastated. I guess what im asking, is that if i have to leave him, how do i do that? And if there is hope...please tell me where and how?What do you do when your Boyfriend wont man up, and be a man?
Time to have a talk with him. He needs to grow up. Good luck*