What does it mean when a guy looks at you like this...?

Ok so there is this guy in my cl. We used to be best friends like 2 years ago... I know he used to like me alot, he even said once he loved me. I never liked him that way. He used to stare at me loads, even though he has a girlfriend. Recently, whenever he has seen me walking the same way as him in the corridor or whenever we see each other, when he sees it is me he quickly looks the other way or looks down. Basically avoiding all eye contact with me. Why? He has a girlfriend btw..