Most Helpful Girl
You can move on, but rebounds rarely work
Most Helpful Guy
do rebounds have to be official? do you mean like officially made known that it is just a rebound? OR official in the sense that she is officially your gf?
I think either way you just play it the way you want. your ex gf shouldn't really factor into your decision aside from the fact that you respect her and not rub it in her face or hook up with one of her friends. but aside from that your personal life is just that, personal, and while it may sting to know you are hooking up with someone it's really up to you.
just try to be discrete and respectful of the ex