There's the big red stop sign, since you're still a virgin, chances are if you go any further with this girl and actually have *** with her, you will probably start to fall for her big time and when she ditches you to go hang out with her boyfriend then you will be heart broken sitting at home on a saturday night from hanging out with your friends. Trust me, if a girl has a boyfriend then stay away if you're looking to try to get into an actual relationship wit her, but if you're only looking to get some booty and call it quits (which doesn't seem like the case), then go for it.