It's a one-night stand. How could it hurt?

Dear Diana,
I am 24 and have been seeing a gorgeous girl for around eight months now. No complaints there. She's everything a guy looks for in a girl and until recently, I thought so too. Until I met this other girl. She's nothing like my girlfriend. She's dark (my GF's fair like a phirang), she's funny as hell (my GF's sense of humour has its limits) and she's got the coolest attitude when it comes to relationships (my girlfriend is a bit orthodox). This other girl wants to have a fling with me; nothing permanent. My girlfriend is very possessive and doesn't take too kindly to me ogling at other girls. I wonder how she'd react if she found out if I were to actually take this girl up on her offer.

Lucky