It is going to be much harder to leave after the baby is born. Especially if you are experiencing spouts of depression now. [Quick Note] I would speak with your Doctor about antidepressants, due to your high stress situation. The chances of experiencing postpartum depression in your situation are higher than most. If you were to experience postpartum depression, having the challenges of a new baby, and a boyfriend addicted to herion, would cause for the lack of energy or shear will to leave. All addicts plan on quitting, the % of those that follow through are slim. Has he even made plans to enter a detox center? He's not planning on just going cold turkey is he? If so, that % I just mentioned just dropped to 0%. Leave, you can always re-enter his life if he follow through and stays clean. Another thing, I can't see a newly recovering addict handeling a new baby. Stress triggers relapse.
To defend your newborn a little bit. Do you, as a mother, think it's fair for your baby to be brought home to a house where someone is abusing and selling heroin? That will be your memory later in life. The first serious decision you made as a mother was horrible wrong. That's a lot of regret. Also you know the answer to your question. Not all children need their father in their life. You probably need him more, but you have to remember it's not what you need any more. Your decisions now, begin to shape and mold your childs life.
Another thing to think about. Babies start crawling within months. What happens if he hasn't stopped. [Some Tough Love]Please think about the consequences... Can you imagine the horror you would feel if your baby injested some heroin that your high boyfriend didn't put up. It wouldn't even take a full bag of dope, just a ripped open, used one with a small amt. left over for a baby to go into cardiac arrest. What if he/she gets ahold of rig and put it in his/her mouth.
From a recovered addict, who it took years to quit, take my advice leave and don't create regret and bad memories with your new baby