Priscilla...
Welcome to the Board. I am sorry for the pain and the confusion that has brought you here, but I'm thankful that you took the step to post. Other members will be by in due course to greet you, but until they do, I'd like to share my own thoughts.
From what you describe, he's got a couple of things going on in parallel: mental health issues, and addiction issues. When you're 12 years old and you're the child of an alcoholic and a drug addict, it's an awful environment to be exposed to. And when it blows up, who's there to take care of him?
I feel for him in that regard. He certainly didn't ask to be brought into the world under those circumstances. But he was. And now, here you are trying to make sense of someone who doesn't understand himself. Hence, the push/pull type behavior. It would not surprise me if he is a Borderline Personality. But to your question --
He stopped before? So why won't he stop now for me?
-- that's not how addiction works. Active addiction is the abdication of self responsibility for the sake of seeking pleasure or, more than likely in his case, escape. So if he cannot be responsible to himself, then how is he going to be responsible to you?
As far as the pain you're experiencing goes...it sucks. It's brutal. It's not fair. And, sadly, it's normal when someone we love is suddenly not there for us anymore. What's important right now, Priscilla, is you have to process his behavior through the dual prisms of mental health and drug addiction. Only then will it make any sense. And once it does, you'll soon come to understand he's not a suitable partner for you.
It pains me to tell you that. But often times, the truth is cruel. What we can do for you is help fill in the gaps of your knowledge, and you can learn from our other members how they managed similar heartbreaks.
Keep posting, keep safe, and again, Welcome to the Board.