Why do shy guys do this? how can i tell what he's thinking?

this guy texts me and we IM and talk about everything. he ususally texts or IMs me first. We talk quite a bit "on texting or IM" we live in different cities that's why. But get this : when he sees me ( cause he has family where i live and our families are friends) all he says is "sup?" and doesn't even look at me when he says it ,then just walks off. But i catch him starring at me. He seems shy because he is ALWAYS like that with me. but he invites me places and really really wants me to go but then acts like that. what do u think? does he like me or not? Be specific please????? "Details".