I say this knowing your request was for prayer NOT advice so first and foremost you and your son will be in my prayers as God wills the outcome to be.
A dear friend of mine (my first ex-wife re-married with 2 kids and now divorced) has experienced very similar situation to you from her son following divorce. This went on for over ten years as living with her gave him easy access to feed his drug habit as he stole and pawned everything of value on several occasions to binge on drugs. She is a very strong and responsible person with strong boundaries in every area of life except with her own children. Sometimes a mother's love knows no bounds as that is how nature programed women and far too many children latch onto this as their god given right to suck all life out of their host.
You are in a situation now where you have been separated which is the best possible outcome for both you and your son. It is the only sustainable outcome. Never stop loving him but it needs to be a tough love he can respect as he learns to stand on his own feet. I've seen the miracle of an empty stomach guild even the most unguided into manhood, it's nature's way of overcoming all obstacles both physical and mental. Live strong and be a light to him.