He’s young, it’s relatively normal for kids to do daft stuff.
When I was his age I went to college for breakfast and caught the bus home. I quit not long after.
Fortunately a couple of years later I go my head in gear, got a degree in computer science and earn a decent wage.
In regards to the drugs, he’s young, he’s probably going to do them unfortunately, it’s not good but it’s life. Have a good conversation with him about it, don’t try to stop him going out with friends, just encourage him to think twice about drugs.
The threats of violence aren’t good though, you don’t deserve to be treated that way. You need to tell him that saying stuff like that is completely unacceptable. Can you go to the GP with him and discuss his mental health issues. I have them myself, hence my self meditating codeine addiction. Maybe they can refer him through the IAPT service for some CBT. Antidepressants are garbage for anxiety to be honest, I’ve tried them all and the only things that work are Diazepam, beer and codeine.
CBT is the best natural way, a word of warning too, don’t let the GP prescribe Diazepam to him, it’s extremely addictive.