If he is as bad as you describe him but 4 other housemates have chosen him over you who portrays herself as a good person, then your story doesnt add up.
Clearly they like him more and are so happy to get rid of you. Let that sink in. By the time your own "best friend" has chosen him over you, then you really need to review your life, It is you with the problem and they are happy to get rid of you for nagging and constantly complaining about things.
You cannot start poking your nose in people's business. If someone does drugs, I dont understand how that is your problem enough for you to be pissed off. This is university and they are adults. He is not a child for you to give him rules. When you live in shared spaces, people are bound to sue your stuff. Its life. No need to whine about it. It is that constant whining and complaining coupled with your temper issue that has made you homeless and friendless.