The best thing about this, IMHO, is that you are spilling it out. That in itself can give you the strength to get through it. Sounds like your ex is an abuser in more ways than one. He's trying to exert power and control over you, and he knows your weakness. But you can beat him and temptation. We are all a community here and I am sending you all the spiritual strength I can. And please please get as much face to face support as possible. It takes a village to raise a child; well, it also takes a village to stop an addiction.
Peace,
Jana