Believe me him living on his own he will just get worse and be having it a lot more.
I can imagine what ever you decide its going to be really hard for you, you either stay with him and hope he does stop.. which he really needs to make a lot of sacrifices. Or like you said be on your own and scared. Its not fair on you with being pregnant and the emotions you go through.
All i can suggest if you want to make it work say its either the coke or you and the baby, or at least he puts in the effort that he wants to stop. Or you do it alone. Which believe me it will be hard at 1st. But in the long run. You will be a lot happier. Have you got family to help you?