Welcome to SR. I am sorry about your son and can relate. My middle age adult son has been living in his addiction for 25 years or more.
For many of those years I thought I could save him. We let him move home when he was homeless, with strong boundaries about not using in our home and that he must be attending some form of addiction counseling/meetings/day programs. We thought if we loved him enough and provided him with a safe, loving home where he could sleep safely, eat well and be "family" again, that maybe he would change his ways and reach out for some real recovery.
All that ever accomplished was to turn our home into a war zone where he (against my knowledge) kept drugs and stolen good and at the same time he stole from us...he stole a lot. Each time it would not end well and we had to make him leave. Usually we tried to help him into a rehab or clean house, but again, that was OUR plan and not his.
In the end it made me very sick, and crazy too. I lost sight of who I was and what was good for MY life and it got worse with every day I lived like that. Like you, I thought he would die if we didn't take care of him.
I joined my own support meeting, CoDA (Codependents Anonymous), found a sponsor and learned to work my own 12 step program that saved my life and brought me back to a life worth living.
My son disappeared for about 15 years and then one day we were contacted by a woman who worked with the prison support programs and asked if he could contact us (she did this through a 3rd party) and after some thought we decided that he could contact us again in 6 months and we would revisit the possibility of talking to him if he was clean and working a good solid program. Sadly, after a month or so he was back at it and now is back in prison for some pretty serious drug dealing charges, not his first time. I was glad we had opted out of the drama this time around. That circus left town a long time ago and I will no longer live a life where addiction exists.
Take a good read around here, especially the "sticky" posts at the top of this forum and you will find a lot of useful information. Also there is a book called Codependent No More by Melody Beattie that has helped many of us understand how we got so enmeshed in a loved one's addition and learn to live a healthier life.
Again, I am glad you joined us and hope you will stick around. I've been here for almost 20 years and find strength, hope and courage here every day.
Hugs from this mama's heart to yours.