I was reading that, thinking,'Did I write this and forget!" My second son had been a nightmare all his life regarding his mental health. I totally identify. Mine was diagnosed with bipolar at 22.
He finally left home a year ago. Thank goodness for us he left on decent terms, having sorted himself out 3 years ago over time. He finally realised that he had to start taking responsibility for himself after the unexpected passing of his step dad (who was and is the dad he didn't have to be)
Whilst I was blessed with his moving out that all happened normally, I hope the suggestions I make now are useful for you.
1/ Aim to keep life in the day (when I added yesterday and tomorrow, my anxiety kicks in). This is, of course, an ongoing challenge. However, it does help with practice
2/ A daily journal/writing and emptying my head of the rubbish in it.
3/ Keep in touch with him. Regular texts, even if he doesn't respond. You're still the parent. Don't get caught up in any drama he wants to start.
4/ Start by once a day doing something good for you. Your mental health is shot through all this
I hope he will come to see his part in things. He is in the blaming game, which shows emotional immaturity.
5/ You have been through hell, and if it isn't fair, I know.
6/ I have 4 adult youngsters. 3 are in my life. 1 of them for no reason. I hear off once or twice a year
I hope this helps