I like this guy and I think he likes me too, but how do I know?

He lives next door to me, and he is always at our apartment for no reason. My roomates and he always hang out together but he is alone with me all the time too. We have stayed up till 3 in the morning several times just talking and watching tv. He doesn’t seem to have a problem with it if I lean against him when it’s just the two of us, and he always makes eye contact with me, and holds it just a little longer than normal. But when other people are around, and sometimes even when they aren’t, he acts like he doesn’t like me at all and picks on and insults me. I don’t know what to think.