What does it mean when a boy does this....?

Hi, so I was really close friends with this guy for 2 years and when we moved to upper school we sort of drifted apart. We have only drifted apart for 6 months and he is hanging round with all the popular people ( most are not nice). We used to talk all the time and we used to joke and play fight and tease eachother (nice way). I would be lucky to get a sentence a week of chat. He started hanging round this other girl who many of my friends say looks and acts like me. She flirts with him a lot! She ruffles his hair, hugs him in weird moments and punches him on the arm ( don't know why?). It looks like he dosen't like all the flirting because when she does it he pulls away and acts as if it never happened. She always does it in religion where me him and the other girl are quite close together. I think she might want to make me jealous because I was once his best friend. He always looks at me a couple of times when he tells jokes to the class to see if I'm laughing. When I look at him sometimes his eyes dart everywhere and he also sometimes looks at the floor. Also when we were on the school field all of his friends were looking at me and he often turned round also. He has changed his appearance as well like his hair for instance. What should I do? :D