Guys: why the hell is he doing this?

so this guy I like (I didn't like him at first but when I realized how sweet he was i started to like him),we're in the same homeroom and grade and everything but the first time we talked was on facebook,and he was like "I think that's the most you've ever said to me haha" and we talked a few times after that,usually him starting the conversation,i started it once,cuz usually when i start conversations I feel like Im bothering them.then I said hi to him in gym,and he talked to me in gym after that.but yesterday he left the chat randomly without saying bye,and he didn't really say much to me today.why is he ignoring me,when usually he talks to me and stuff? i know this sounds obsessive and stupid but I really like him.