I see a lot of myself in your post here. I too cared deeply for my son and wanted only a healthy normal life for him..but it was never mine to control.
I learned that I could live in the problem...his addiction and my worrying about it day and night, living in fear for what might happen to him, or I could live in the solution...my recovery and learning to let go and find a healthier way to live my own life, regardless of how he chose to live his.
After living in the darkness of addiction for too many years, I chose to live in the solution of my own recovery. I went to meetings, I took long walks in nature and took time to notice the beauty that surrounded me. I found a hobby, photography, that took me outdoors and gave me something special to pursue in my own life and I met people who shared my interest and helped me grow into someone who embraced life instead of fearing death.
No matter how much you love your grandson, he will grow at his own speed, make his own decisions, good or bad. You have done your part in raising him, now it's time to give him the dignity of finding his own way.
Hugs