Dear Ocean Lady, I am sending big hugs. I know this is a hard path but you state many truths in your posts. Letting go is the beginning of your recovery. You can even tell your son you are done, but you MUST put actions behind it. I think once we pull away, the final realities begin to set in. My son spent 9 months in jail between September of 2012 and July of 2013 because of his choices. He turned 23 and missed Thanksgiving, Christmas and New Years of 2013 because of his actions. I think he finally understood that he would continue to miss out on life's events and that time gave him some perspective.
Once you son gets into rehab, it is wise if you are able to DETACH. You can be there for love but not so much for face to face support, etc. He needs to choose his path.