So sorry to hear how things worked out. Hopefully after working in a grocery store for a while, seeing how hard it is to make ends meet, watching his college friends moving forward while he is in a dead-end job (if his college friends even want to still hang out with him) will quickly inspire a change of heart for your son.
No parent does everything right so don’t kick yourself for things you would do differently. At this point your son must start to take responsibility for his life.