Missed the beginning of the movie...
So maybe I missed something important. What exactly was Sarah so bitter and angry about? I didn't really understand where she was coming from. It seemed like the entire movie was simply her throwing tantrums over almost every single thing her boyfriend did. I found her behavior rather inexplicable and hysterical to the point that aside from hot sex I have no idea why he even wanted to be with her at all so I'm guessing I missed some rather important character establishment at the beginning of the movie.
It wasn't me who was murdered, was it?