Well, Paramore said in an interview (which is in an magazine I forogt the name of) that it is the opposite song of Decoy.

CrushCrushCrush is about "her" being in love with someone, who doesn't really love her, just play with her. But she doesn't care, she plays his game too ("if you wanna play it like a game, well come on, come on let´s play"), cause "she rather waste her life pretending, than have to forget him for one whole minute"