Is he flirting with me?

Well, he's definitely flirting with you, but that isn't necessarily a bad thing. Flirting doesn't equate to "trying to start a relationship" or even to "proposing sex." If he's attracted to you, he probably can't help behaving that way.

Now, if the reason that you don't want him to flirt with you is that you are attracted to him and don't want to end up in a situation where you are hurting because you want him but can't have him, then you should certainly tell him. Remember that if things become awkward, that's actually a good thing! You aren't going to be falling in love anytime soon when you two have some dissidence between you.

I guess the best advice would be to weigh out what the effects of his flirting are. If it looks like either you will get hurt or he will end up cheating on his girlfriend, then I would recommend that you tell him to stop (and of course, you can word it diplomatically so it doesn't come off as being angry or unfriendly). If it is just harmless behavior that is a little more cute than the usual boy/girl interaction, then there's probably nothing to worry about.

yes, sounds like he's definitely flirting with you. he seems to be doing it in a very obvious/ outhere kinda way aswell which is odd as you say he has a girlfriend. It sounds to me like theirs something else going on that maybe you not aware of. alternative motives maybe, or whatever it may be you're absolutely right when you say you want to tell him to stop. even though being flirted with is always nice, it will destroy friendships and relationships in this case. you didn't mention whether or not you no the girlfriend? if yes,then maybe he's doing it to make her jealous.? and if not, then perhaps he's just not as nice a guy as he seems. talk to him. when he starts doing these things again then randomly bring it up very casually. that would be the easiest. because then at least if it is nothing, your friendship will still be in one piece.