I couldn't have prevented any of these possible scenarios when my son lived with me anymore then I can prevent it now that he is living on the streets.
Behaviors such as:
Suicide attempts, overdosing, driving while high and drunk, getting in fights, getting fired from his job, failing college, breaking the law, risks of contracting diseases through needles, and using.
I think it was OutToLunch that said the only way would be locking him in a cage and watching him 24/7.
You have stopped helping him to use. Your actions are truly loving.