Hi welcome. I'm sorry for the tough spot you find yourself in. I know you wish he would follow through on his promises but he hasn't and empty threats won't make him change. Sometimes it's hard to accept that we have no control over the choices of another human being. The only thing we can control is our own behavior, and our responses to other peoples behavior.
I gave him an ultimatum (after he nearly OD'd) that if he took any more xanax, he was out of my life for good.
Now you need to decide whether you are going to follow though on your words, or if you are going to continue with his addiction game.
Focus on his actions, not his words. Because words are meaningless when it comes to addiction. They lie. Saying you are going to quit or saying that you WANT to quit using is not the same as quitting. Not by a long shot.
It might be helpful to ask yourself, by not following through on your ultimatum to leave if he continues using, what are your actions telling him?
Do you have any family nearby that you can turn to for some support? I hate to see babies grow up in a house full of addiction and dysfunction all for the sake of a few dollars.