Can someone help, my friendship with this guy may have changed...?

Hi,

I was at a week long camp for my school and this guy I know started to act differently around me than what he was like before. We were friends before this started to happen and I honestly can say I have no idea why he started acting like this because he already has a girlfriend that I know he really likes. ANYWAY, during this week he started winking and grinning at me as he walked past. He also just said hi to me when their were clearly others around me. He also started to talk to me more often than usual.

This is so out of character in our friendship and it is starting to freak me out as I don't want to change the way things are. Can you please tell me what I should do?

Thanks