I always say this in these situations. Your in a real hard situation.. hes your son.. there no greater love than the love for your child.
And from what you have said hes making your life hell. No son should make you that scared you have to lock yourself in the room. He should be protecting you if anything.
Does he want to quit the drugs?
Your asking how can you support him?
I really dont know in these situations.
Some people say. Leave him to it.. he will have to learn for himself.. then if anythimg happens you will blame yourself.
Or u can let him back and say. No drugs you sort your self and thats it or your on the streets again.. which you probably know he will be the same again.
Id probably support him.. by making sure his staying somewere or got warm clothes. And buy some food for him..dont give him money.
What do you want to do?
Is he your only child?