I'm sorry you in this situation. I was in a very similar situation in my early 20's and spent 5 years trying to fix him and get him to grow up. I finally realized that it wasn't up to me to fix him and I had to either accept that this would be my life of wondering at 1:00 am if he was okay, if he was cheating, if he was driving drunk, etc or get out before I ended up pregnant.

You do not do anything to make him take drugs or drink. If he says that, it's just an excuse. You want a partner, not someone you have to mother and he acts like a child. Life is too short to deal with this disrespect. Good luck.