The Edward Cullen effect is when your girlfriend/boyfriend breaks up with you for somebody that does not exist. This is named after Edward Cullen from the Twilight series, as many fangirls broke it off after she "wanted somebody more like Edward Cullen."
Girl: I'm sorry but...I'm breaking up with you.
Girl: I just want...somebody more like Edward.
Guy: (Later) She dumped me for somebody that doesn't even exist...what a douche bag.
Guy2: That's the Edward Cullen Effect, man.