MamaB, I know how you feel you are not alone there are many of us parents here who have felt the same. I have 2 sons who abuse substances for a long time I felt guilty I now know it wasn't my fault. You didn't cause it, You can't control it, You can't cure it.
I became very sick from worrying, blaming myself, trying to save my sons, etc... I had gotten to a point where I either could not sleep or would sleep all the time my thoughts were always on them what can I do etc...
I in time learned what I could do was take care of me something I wasn't doing.
Get enough sleep don't over sleep
Eat healthy or in my case in the beginning just be sure and eat
Keep my house tidy to MY liking
Shower the simple things most people do that I was not doing daily.
I found this site and then I started Ala-non as there is no Nar-anon in my area.
I also read Codependent No more a book my Melody Beattie
I will be praying for you and your precious son.