You aren’t going to get this kid back in to the “cage” of his old lifestyle. Once you have experienced certain things, you can’t go back to the old status quo.
Best case scenario is either him defecting to (in your eyes) a lesser form of “yidishkite” or becoming a well adjusted adult with no use for organized religion.
Keep the lines of communication open and keep trying to develop an adult relationship with him, it will work wonders.