So I have been seeing this girl casually for a couple of weeks now. We'll call her hippie. She fun, hot and is open sexually. We aren't per se "dating" but we hang out quite a bit.

Tonight, I end up getting a text message from one of my old serious college girlfriends and she ask "weird question, you dating anyone right now?" I answer with "nothing serious, whats up?" She begins to tell me that she has been single for a month and is looking for some instant gratification. I tell her yea sure she could come on up and we could have some fun. She sends me a whole shit load of sexual texts message, telling me all shorts of awesome-ness and to send her a picture of my dick. So I play the game and send it. She then responds, "so we are both young and experiment, its been long enough that there is no more emotional connection, do you happen to know any hot girls that would play with both of us?" After I do ten back flips, I start thinking who could I ask. And the only one that I would really like to do it with is hippie.

Hippie has no idea who this old girl is, what we had beforehand. So question is, would this be a good idea? Would it just sour both relationships? Is it worth it to sour both relationships? I have a few other girls that might be down, but they aren't as hot as hippie.

Help a brother out.

TL;DR: Cute ex-girlfriend wants a threesome, have current cute girl that I am seeing casually, should I try and make it happen or use another less hot girl that doesn't mean anything to me?