Do you see that you're doing the same thing as your son is doing?
His stance is this: Unless you help me, do for me, I will not survive. (to paraphrase)
You seem to imply this: Unless you stop threatening suicide, using drugs and alcohol, act like a normal human being, which is rationally, I will stay trapped in this cycle.
Each of you is acting helpless. Your life and well-being are NOT contingent on what he does or does not do. You do not have to be miserable, fearful, helpless, and consumed by this situation. This is a choice. We do not have to feel and act as if our very lives depend upon what our ADULT children do or don't do.