Writer, I'm sorry you're going through this, and I hope he gets it together soon.
I will tell you that fifteen years ago I made two decisions that made my parents completely despair for my sanity and my future-- I dropped out of law school in the middle of the first semester and I got divorced (only person in my entire family to divorce in the absence of substance abuse or violence issues). My mom thought it was the end of the world, wanted me to move back home RIGHT NOW, lost lots of sleep over it. But I knew my heart and I adore being a nurse, I'm happily married (ten years next month!), and we have a beautiful family. I had to stop trying to be the person I thought I was "supposed" to be to have enough room to become the person God meant me to be. No matter what your son decides right now, it may be in service to a better future than either of you imagines. Good luck to both of you!