Does he like me?

okay well there is this boy. we both are in band cl together. i have been talking to him for a while and i really like him. he flirts with me like he says he's a big flirt and a couple of times he waves to me and i wave to him bak. he even asks like he forgets my name but i no he remembers it. we even walk to homeroom together............but the wierd thing is he has a girlfriend. why is he flirting with me like that and he has a girlfriend. should i just wait and see if they break up when school starts or should i just leave him alone foreva.