My opinion in this, ( if you'll hear me out and let me play the detective ) is there's a hopeful part of you that sparks would fly. For one, you were at a friend's party with a lot of your friends. You were among friends. Unless none at the party are really your friends, I would think you have more than someone to hang out with. For two, why among your guy friends did you call guy B? Well, let's get to the obvious. You wanted to hang out with him. You like him and have liked him for a while. You said so yourself. But that's perfectly fine. The only thing was the order of events that should've happened. Instead of breaking up with guy A first, you were caught by a spur-of-the-moment and moved on to guy B. You were caught in one relationship while at the start of another. But now that you've broken up with guy A, why do you doubt your decision? Why aren't you sure whether you should've broken up with guy A? Because it's never worth it to give up one relationship for another. Unless it's a failed relationship to begin with, you're giving up what you have for what might be. You give up what you know for what you're now wondering about; How much does he like me? Does he like me enough? Out of this uncertainty, you wonder what you should do. Well... all you can do is move on with your new guy and hope there won't be a guy C.