Lynn. P, thank you for replying to my post. I am male. I only know that our parents and grandparents never had any mental illnesses. But I don't know about the rest of the family.
I am sorry to hear about your brother. Do you mind if I ask, if there were any similarities in his behavior when he was developing bipolar, and whether it happened suddenly?
As far as I know, he never did that kind of drugs, he only takes the sedatives. I've asked him where he gets them from but he just rudely told me to mind my own business. When he leaves the house sometime, I'm going to find them all and threw them out, I've had enough of his attitude.

It's impossible to put a lock, since we actually share a bedroom. It's pretty spacious therefore 2 beds fit there with no problem. I live in a 1 bedroom flat and can't really afford anything else now. I'm not afraid of him, or anything of that sort, especially since I'm a lot stronger, but still, as you pointed out, it would probably stop him sneaking into my bed at night.

ickydog2006, thanks a lot for your input. As some of you suggested, once again, I've tried to confront him about all the issues. Unfortunately, as expected, it was impossible to have a civil discussion with him. When I asked, if someone did something to him, he got really angry and yelled that, I will quote his exact words 'You're the one that makes me go mad'. This is completely ridiculous.. He wanted to move in, I agreed, and now he complains, even though all I'm doing is trying to help him.
I lost my patience with him, again, and told him to go pack his stuff, because he's moving back to our parents house. Of course, I didn't mean it, but he probably thought I did. He locked himself in the bathroom for hours, crying. Really, I didn't expect that, I didn't think he would react this way. Before that 'personality change' he rarely ever cried, only when he was idk, like 7 or 8. Now he does it a lot. Since our argument (it was like 6 hours ago), he refuses to speak to me and just went to bed now (this time, fortunately, his own).

Sorry if my posts are too much of a bother but it makes me feel better to talk about this, and somehow, I can organize my thoughts better when I write it all. Once again, thanks for all the support.