I have a friend me and him are not really close but we used to smoke/chill /play 360 (regular ****) with all of our friends..he wasn't in the circle though..
Well i seen his girlfriend the other day and she works at a clothing store by my house and we talked for a bit and before i left she gave me her number because she said it's weird that i'm her "friend" and don't have her number and don't talk much.(weird because i never considered her a friend)
well I texted her so she could save my number and she's been flirting here and there with me

and well I know she's attracted to me cuz she'll say stuff like you're cute and say that out of his friends I'm the best looking.

Anyways, I'm thinking I should take this to another level with her and at least hook up with her..but I feel a little guilty doing this behind his back but then again if she's willing to do it too then **** it right? any advice?
What would you do?