17 year old stranger in place of my son

I’m at a loss as to know what to do for the best. My son is 17 & addicted to Ketamine but will take just about anything to get wasted, valium bottles rum and so the list goes on. I have real concerns for his safety. He was arrested a couple of nights ago for criminal damage but doesn’t care and has been on a permanent bender fir weeks. Sadly tonight his Dad hit him and cut his lips as he went to attack me this has made his Dad feel sick and im worried he won’t be able to be involved as he knows he has overstepped the mark and never wants to be in that position again. He doesn’t live with us so we will be on our own. So tonight I find myself camped outside my son’s bedroom in a sleeping bag checking he is ok every half hour after we settled him enough to sleep off tonight’s rum and ketamine. I’m at my wits end he doesn’t want help so no one will help and I can’t stand by and watch him kill himself (as well as the obvious threat to his life when he gets in a state he says everyone hates him and he wants to die) I’m heartbroken any advice would be gratefully received.