Yes, I believe it's a good idea for you to disengage from your sons choices. You've reached your bottom it seems. Often we parents reach our bottom way before our addicted or mentally ill adult troubled kids do. We burn out. They, on the other hand, are usually well cared for by us, so the desire for them to change or seek help is completely gone. Unfortunately, we can't sustain that level of enabling for long before our own well being and our health become extremely compromised. Boundaries are the answer. Boundaries are what you are willing to do and what you are not. You are no longer willing to have an abusive, manipulative, nasty man hold you hostage in your own home. You appear to have awakened from the FOG (fear, obligation and guilt). Good. You matter too. You deserve to have a peaceful home which you can call your sanctuary. I would encourage you to continue down the path you've chosen, hard as it is. I am a very soft hearted person as well and I have had to make remarkably difficult choices around my adult daughters behaviors and choices which are detrimental to me. We don't do our kids any favors by protecting them from the consequences of their behaviors, we in fact, help to keep them stuck.
I needed an army to help me out of the enabling maze. It is near impossible to do on your own. You might try contacting NAMI, the National Alliance on Mental Illness. You can access them online and they have excellent courses for parents which can offer you resources, information, guidance and support. Give them a call if that feels right. Many of us here have private therapists or counselors or parent groups where we can go for support, to be heard, to get guidance and help in setting boundaries and keeping them. It helps in many, many ways to receive support. This can be a lonely path where no one knows the profound heartache we parents feel when our kids go off the rails for whatever reason. Here, we know. We get it.
You may want to read the article on detachment at the bottom of my post here. You may also want to read the book, Codependent no more by Melodie Beattie. Keep yourself armed with support on every level.
Hang in there kat, please start to put yourself as the priority. You've taken care of all of your kids, now it's time to take care of YOU. You've done enough. Your son must develop the desire to help himself, without it, there is nothing anyone can do for him. He has made it pretty clear that he has no intention of changing at this point. But of course, his staying the same is completely dependent on your willingness to allow it. Don't. Remember, we are treated in the ways we allow, don't allow anyone to treat you without respect and dignity, most especially your own son.