Chloe
(2010)

Catherine hires Chloe, a prostitute to see if her husband david is Cheating on her.

Chloe tells Catherine that he is cheating on her, so Chloe and Catherine become closer and eventually have sex.  

It is revealed that David never cheated on Catherine and Chloe was lying.

In a fight at Catherine's house, Chloe breaks a window and purposefully falls out because she cannot accept the fact that Catherine does not love her. 

Thanks Peter!