I’ll start. Teenage me driving up the street to hang out with friends at the mall and passed my younger neighbor and his mom. When I got back a couple hours later, the neighbor’s mom was livid - confronting me for the slight. I seriously had no idea wtf she was talking about and I couldn’t convince her otherwise.
Sorry to hear that. I know what that’s like. The best you can do is keep up the reassurances and hope he can make it through this rough time. Encourage him to go to therapy and maybe get medication. In the end, change is up to him. Good luck.