How do you know if a guy likes you or if he is just being nice and you are a freshman and he is a junior?

Not being able to tell the difference is one of the most frequent reasons why two people who like each other don't get together, and unfortunately it will always be, because telling the difference is usually very hard. There is no easy way to find out whether he likes you or is just being nice. If he gives you the impression that he likes you then there's a chance he does, because impressions come from subtle signals. However you might just as well be mistaking things he does for such signals.

It might help you a little to think about what kind of boy he is. Is he the kind that would just be nice to every girl because he's simply a nice boy? Or is he treating you in a different way than all other girls?

However if it seems like he might like you, watch out very much that he's not only playing you. He might seem like he really likes or even loves you while actually he only wants you because of your looks or your reputation, or even worse he's only up for sex. So don't let him get anywhere near underneath your clothes until you know him really well, as in you've become a part of his life.