Just Broke up already have someone new, what should i Do?

OK so i broke up w/ my gf about a week ago. now before and the whole time we were together there was this girl who always had a huge thing for me but i never let anything come of it bc i was with someone. So now that we broke up ive started kind of talkin to this girl now. Im not really sure i want a relationship wih this girl, but def wouldnt' mind just having some "fun" atleast for now. so what should i do. she is a really nice girl.