BTDT, survived. And by survived, I sucked it up until college, then my life really began. Mom was in depression most of her life, and dad was a workaholic, so neither did anything to help. C'est la vie. I've never been back to a high school reuinion, could care less as that part of my life is a total write-off.
Try to help him, tell him he's loved, do what you can. What worked for me was going to college far away, at total life reset. Maybe not private school, but maybe a magnet school, those schools tend to be filled with a better cut of kid, certainly more in line with your son's values. Whatever it is, don't stop trying.