I want to leave my son’s father

My boyfriend and I had our baby boy on 8/8/18 and it’s been quite a rough couple weeks. My boyfriend never wanted kids but he eventually seemed to come around by my second trimester. I thought I couldn’t have kids, so my pregnancy was a shock to the both of us. Ever since our son was born, he hasn’t really been a team player. We don’t live with each other, we were planning on it after I get a job (I graduated in June) and we live with our families. He comes over every other day or every 2 days to help out for a few hours and then goes home. He gets 10+ hours of sleep, which I’ve come to resent him for. Another thing is that he’s a big smoker (cigarettes and weed). He is a complete jerk when he goes too long without a cigarette. One time when our son was crying and he had gone about 3 hours without a cig, he stormed out and said “I thought my life was a living hell before having a child, boy was I wrong!”. The last straw was when this happened: we planned for him to come over one night and he said he didn’t want to come because his dealer was coming later. I said too bad I need his help and he said “Fine I’ll come tonight but then you better find a different boyfriend”. And I was completely shocked. I was so mad and hurt that he would throw away 4 years of being together because he didn’t want to help. He’s been really irritable lately and having a hard time adjusting to parenthood. Those are just a couple examples of things he’s said to me over the past 3 weeks. I want to break up with him but I’m scared of being a single mom and I don’t know if it’s too soon to decide whether we would be better off apart. Thoughts? I just don’t know what to do.