Sorry to hear this, it sounds like you’ve had an awful time of it. I’m not in the same situation but can relate in small ways as my mum has had addiction problems with alcohol and prescription meds. Also an ex used to smoke weed and had anger issues. But in my experience these people don’t change unless they decide it’s something they want and they don’t consider the harm they are doing to others, just as long as they can meet their own needs. I know it’s not easy to consider letting somebody go, who you care/cared about but in these types of situations people will usually continue to have the same patterns of behaviours and it’s far better for your own health if you leave him because you can’t force them to change. You can try to help by offering to go to the doctors with him or helping him make phone calls but it still may be best to call time on your relationship and live separately. At least if they know that you have no tolerance of it anymore then it gives them that bit more incentive to give up if they want you in their life. You can not allow yourself to be treated like a mug. People who know that they can mug someone off will continue to do so. Think of you and your child as you need to put yourselves first. He is a grown up and needs to be allowed to make his own choice, for the better or worse.
