What should I do about this guy! PLEASE HELP! I really need an answer! :(?

First of all, STALKER much? (him, not you) Sorry but I just find it creepy when guys like wander "back and forth" probably eavesdropping just because you were talking to your guy friends. But anywayss, if he has a girlfriend, then he's definitely a flirt. I personally don't trust him because he might want a fling or something and if he ends up dating you then he might cheat on you. I mean, seriously? He flirts with another girl too? But I'm kind of an insecure person that worries about everything so whatever. It really seems like he likes you because of his friends and all. If you really like him and you don't mind dating him even if he has a girlfriend, then I say go for it :D But don't be all like, flirting on full throttle or anything, it might seem desperate. Just play it out and flirt a bit.