Does he like me??????

i really like this guy, he's a junior. and i'm a freshman. i met him at the beginning of this school year (august 2009). i just started talking and getting to know him more, like in the past month. we talk at school and sometimes he'll text me. he has a girlfriend and he's been dating her for almost a year. i've asked him about his past relationships, and he looks thoughtful, like he's thinking about it. but then just brushes it off. i don't know if he's subtly telling me anything, maybe because he has a girlfriend. but sometimes he wants me to do stuff with him, like help him study, but we ended up just talking the whole time. i know this is a little confusing, but how do i know if he likes me without directly asking him? are we just friends?