googley, thank you for your input. Like suggested, I've tried speaking to him about the nighttime issue again, during the day when he was relatively calm. I asked him directly - why. He just said 'because I want to'. Honestly, I'm really trying hard to be patient with him, but that kind of attitude just drives me insane, he acts like such a brat sometimes. I've told him, managing not to shout at him this time, that this has to finally stop, and he can't ignore my words anymore. I've asked him, how can he not be disgusted or ashamed with himself when he says that sort of thing to his own brother, because I really wanted to have at least some answers. I thought that it may at least give some hints on what his intentions are, provoke him to talk. But after I said it, the talk was over, he refused to speak to me and didn't even reply. I'm fairly certain that he won't stop just like that. Is it, in your opinion, okay to use physical force in that case?
You've asked whether he's emancipated - no, he isn't. I'm also not his legal guardian, it's sort of a family agreement.

Sam2, once again, thank you for your time and effort. I understand now, thanks for clearing that up. I wasn't sure if something like that was possible (with sexual abuse in the past), so I really appreciate that you gave me some insight on it.
If it actually happened to him, I doubt he's ever going to tell me, no matter how much I try to make him talk about it to me. So I'm not sure if I'm ever going to find out what really happened.
I understand that he should see someone, but he just doesn't want to. I think he's the most stubborn person I know. I will keep trying to make him see someone, even a counselor, though.

Why do you think that throwing the drugs out is a bad idea? I don't think he's addicted, not yet, it hasn't been going for that long. That's why I believe I need to make it stop right now.
But you know, it really makes me wonder, who actually sells it to him. Sedatives aren't really hard drugs, so I think it may be someone from his college, I don't think it can be anyone dangerous (or maybe I'm just naive).

You are right, in the end, I have to make the decision myself, but still, I find all the advice I got from you lot very valuable, I'm really grateful for all the support.
I think it's actually a good idea, I might see a counselor myself, for now, just to see what he thinks about the whole situation. I've been also trying to find some more info about mental health online but to be honest, it just irritated me. I went on the royal college of psychiatrists website, section expert advice, young people. And the first thing I see is this :News:
- childhood sexual abuse may be important cause of schizophrenia
- pupils with top grades four times more likely to develop bipolar disorder
It's like, everything we've discussed here but they state it all as if these are certain facts... I don't know, it just upset me a bit. I really want him to be ok, I keep hoping it's nothing serious but everything hints otherwise. I feel guilty, that something must have happened to him when he was under my care. After all, he's still underage, so I'm responsible for him. And look what happened...

Something really needs to be done, and soon. I've developed a little plan. I don't know if this is the right thing, but I thought I will share it with you lot anyway, maybe some of you can add something to my list.
1. I can take 2 weeks off work, so from tomorrow, I will be home 24h/7. I know that 2 weeks isn't super long and I can't expect miracles, but I want to see at least some little changes.
2. No more skipping college for him, I will make sure that he attends every day. I will drive him to college myself, and then pick him up. I will ask his tutors to call me if he's skipping, hope they will cooperate.
3. When he's away tomorrow, I will search for all the drugs and threw them all away. He can't keep taking them, they are strong medications, he can't take them without doctor's supervision. I will tell him, that if he's got anxiety/sleeping problems, he can see a doctor, and they will probably prescribe sedatives to him.
4. No pocket money... And I will take away all his savings from him. I know it may seem a bit drastic but that's the only way I can stop him from buying more drugs.
5. Absolutely no bed sharing... Not sure how I'm gonna do this yet. Maybe I will just use force, like I said earlier. He just can't keep doing this. Of course, I don't mean fighting him but I will drag him back to his own bed if I have to.
6. Keep persuading him to see a psychiatrist, without being too pushy, offering comfort and trying to make him realize that I do care, even though my actions may not be pleasant to him.

I don't want to be too strict to him but I need to take some control back, he can't just keep doing what he pleases. I know that he's going through tough times but I think this is for his own good. I will let you guys know how things are going sometime soon. Also, thanks again, for listening and for chatting to me, I really appreciate all your posts.