chicory,
I make honest effort to not tell people what I think they should do, but I think you really need to go to Al-Anon. I think you are stuck in a seriously toxic, debilitating situation, and until you make true effort to work on yourself, you will stay that way. I am very sorry that you are stuck in this, as my own Mom is stuck in this with my very sick brother.
Your son is sick and toxic and it is affecting you and your life in very bad ways. This stress is going to also make you physically ill if it has not already. Medical research shows people who report high levels of mental stress are twice as likely to die from stroke or heart disease than those with low stress levels.
He is not going to get better until HE decides to get better, and the dynamic between you two is sick. You are asking questions about how to make a sick relationship into a non-sick relationship. It is impossible. And until you decide to step OFF the merry go round, until you decide to get well, until you decide to stop the madness, it will never stop. I am truly sorry and my heart aches to say this to you.
Please take care of yourself.