He definitely doesn't like me, I mean what guy just stares at a girl without smiling and then waves like he did. ...
We get guys on here All. The. Time. who stare and stare at women, hoping the woman will somehow, some way, figure out that they like her.
I don't see any difference between this guy and any of them.
If this guy is too shy to say hi, and if you are interested, then go up to him and say hi sometimes. You go to the same school. You change classes at the exact same times. At some point, you're going to run into him in the halls.
If you're not interested, then be A LOT more direct about that. As in, if you need to create a sign of your own, just have it say NO in large, bolded letters and hold it up the next time he stares at you. Don't waffle, don't try to reel him in only to dump him later.
If you're unsure, then keep on waving. But don't say he doesn't like you.
He likes you.