Welcome aboard Newbie.
I am so saddened to hear your story and the mental anquish you are experiencing.
Your son is vulnerable for sure and you be thankful he has someone like you in his corner. You clearly love and care for him and from reading your post That is not in question.
Disability, mental health and drug misuse is some serious issues to be trying to manage. Any one of these issues is a tall order. You need to be kinder to yourself it maybe that according to your son you cant do right for doing wrong. But thats not true. Not even for a second.
It hard to change someone who does not want to change.
You dont need to give up on him, just be kinder to yourself.
If we change our behaviour it can help to change his.
I know that your focus is HIM but there is no quick fix.
Treat yourself and do something for YOU asap.
I know it might not be how you feel but as they say “Fake it until you make it”
Go a walk, play music, keep posting and phone Adfam to get support for yourself.
Do everything you can think that will refresh your body, mind and soul. Keep doing it and your respite, healing and restoration will start to happen bit by bit. minute by minute.
Then you will get more times when you are physically and mentally stronger.
We are listening, we will walk with you, where and when we can.
Take care