Sunshine, first of all, hugs. This is so painful.
Your question is a complicated one, and one I've grappled with many times. I wish I had an answer that I could live with, but I don't. I'll explain my situation and you can take from it what you will. If nothing else, maybe it will make you feel less alone
My son is much older than yours. He's 26 now. As a child he was somewhat difficult (didn't sleep as a baby, threw tantrums often etc) but he was never in trouble at school or with the law. Apart from struggling with a mild learning disorder, we thought he was doing okay - a wilful child, who was much harder work than our other kids, but nothing out of the ordinary.
Just before he turned 18, things got worse. His moods were worse than ever. His personal hygiene deteriorated significantly and I suspected he was smoking pot. His then girlfriend (who was lovely) told me she was worried about him. We tried to get him to go to a psychologist but he refused and no amount of pleading worked. His state of mind was not bad enough that we could force anything on him (as in he was not in immediate danger of harming himself or others) so there was simply nothing we could do.
Eventually the girlfriend left (who could blame her?) and he did then seek help. He was medicated for depression and he saw a psychologist for about a year. He seemed better, so he stopped going and stopped the medication. Since then it's been a merry-go-round of him behaving badly, seeking treatment, seeming better and then the cycle begins again. I know he is not well but he has proven time and time again that he can exercise self control and make good decisions when he chooses to. For example, he knows that smoking weed is not good for him and yet time and time again he goes back to it.
I'm not going to go through all the ups and downs we've had, suffice to say he does not live his life according to our values. I believe in forgiveness and redemption and unconditional love. Part of me will always love him. However, I also believe that we each must take responsibility for our own actions. My son (and no doubt yours too) has been given every opportunity to live a good life. He's had a safe and loving home, a good education and many rich life experiences - all of which he has wasted.
I live my life exhausted with worry. I want to be free of this but it's not that simple.
I have not cut ties with my son, although a large part of me wants to. As I said, I love him, but love only goes so far. If I'm absolutely honest, I do not feel the same way about him as I do about my other two children. He's worn me down and eroded some of my feeling for him. Now the predominant emotion I feel when I see his name flash up on my phone, is fear. I think,"What now?"
So how do I handle this? I try to keep him at arm's length. I do not contact him, I wait for him to get in touch with me. Sometimes he's in touch frequently, other times not so much. I don't get involved in his life - no financial handouts and he knows he can't live in the family home ever again. I still do some things for him. Like last week I took him to the oral surgeon to have his wisdom teeth removed. I drove him, waited for him and made sure he had the pain killers he needed etc.
He has been better these past two years (that's not to say they have been two incident free). He got an apprenticeship and is training in a trade he enjoys. His work seems to be going okay. He lives independently from us (in a house we own but he pays us rent). He has a nice girlfriend. He seems to argue with one of his housemates a lot and this concerns me, but I don't get involved.
On the surface he now looks like he is doing well. But underneath the facade of normality he still has issues. He's selfish and seems unable to regulate his emotions properly. To my knowledge, he is no longer seeing the psychologist, so I figure it's only a matter of time before he goes off the rails again. I live in fear of what might happen.
My solution to this long term will be to put physical distance between us. He lives in the next town to us and it's a small community so there's really no escaping him. Everyone here knows everyone else's business. My husband and I are planning to move to the other side of the state as soon as we can. Realistically, we probably can't move for a few years yet. My husband is planning to retire in about 5 years time and at this stage it looks like we won't be able to move before then. It's a long way off but even so, the thought that one day there will be a lot of miles between my son and us is a relief.
So I understand. Nevertheless, your son is still very young and there's still hope that he will turn his life around. I hope this is the case. I guess what I'm saying is you can lovingly detach from him and not enable his behaviour - and it sounds like you're already doing that - without closing your heart to him entirely.
I hope this makes sense.