7. Your new girlfriend and your ex will never get along.
I'm not saying that your ex-girlfriend isn't totally open to saying hello or even buddying up to your new significant other, particularly if your breakup was a non-venomous one. But the chances of both your ex and your next girlfriend sharing the same forward-thinking philosophy? That stands about as good a chance as your next girlfriend being Kate Upton.
Marnie makes a scene at a party in Brooklyn when Charlie (Christopher Abbott), the boyfriend of four years she dumped just two weeks earlier, introduces her to Audrey (Audrey Gelman), his new girlfriend. Awkwardness ensues.