I think some excellent advice has been given in this thread. It is hard for many first time parents, even if there are no outside challenges like drug use or a bad relationship. Parenting is never easy, i'm sure it only gets harder as they grow up.
I am certainly not perfect either, and I have done my share of drugs, but I never do this around my daughter. She deserves to have a positive home environment to grow up in. So many of us here didn't have that...
Perhaps you weren't ready for kids yet, or perhaps you just regret choosing the partner you chose. Either way, figure out what would make your situation better because it would make your child's situation better by default.
Sounds like the first thing you need to do is decide if you want to be with the person you're with. If not, find someone else or go it alone for a while. If you do want to be with him, then you need to take action to help him do something with his life and be a good parent. If he isn't willing, go back to the first plan and find someone else or go it alone for a while... Never easy, but always possible.
Might be scary to make a change, but it's even scarier to think of what could happen if you don't change anything...