Nah, he's the reason he's in huge trouble. This is absolutely not your problem in any way, shape, or form.

And now I feel like I just betrayed him

He betrayed you. He betrayed your parents, and he betrayed his family, and he betrayed his school. He also betrayed all the other high school students he's fucked, too - I'll throw my favorite cat out a window if you're the first, but thanks to your so-called "weakness" you might be the last. And that's good.

As for therapy...Honestly...I dunno if it will be helpful for this particular one of your concerns. What he did was fucked up in a way that you'll come to understand without therapy, when you're in your mid-late 20s, been on your own a while, and then suddenly run into a gaggle of 16-17 year olds.

Therapy in general, though? When you're feeling suicidal? Yeah, jump on that while you're still on your parents' insurance. You might have to hop therapists a few times to find someone you click with.