As Cain is saying, just because he mentioned the girl doesnt mean he wouldnt cheat on his girlfriend. Thats how the game goes. There's guys who think if they mention that they'd be around a girl that is gonna try to get with them to their girlfriends would make them look like they have no intentions on cheating whatsoever, when in reality it is their initial plan. Some guys really do think this works, and it actually does work sometimes unless the girl is using her head. But, in this situation, I see it as him just trying to see her act jealous. But, like ecojeanne was saying, play it off. As much as it may burn the hell out of you inside(it sure would bug me out) you gotta play it off as if it didnt phase you in the first place on the outside. He might admit that it pissed him off that you didnt react about his comment (speaking from experience)