This is the kind of movie you'll either love or hate. I loved it. In order to appreciate all the twists and turns, you have to relate to the personalities of the main characters.
Darcy is strong willed and used to getting her way ... She KNEW Rachel really liked Dex. She KNEW that if she put Dexter and Rachel "on the spot" by forcing them to step out of their comfort zone, she would manage to "get the guy" .... For Darcy, it's always been competitive (hence her lie about being accepted to Notre Dame) Rachel finally admits that she's responsible for allowing Darcy to always get what ever she wants ( she tells Ethan in London)Rachel truly realizes that it's not Darcy's fault... But when Dex calls off the wedding, Rachel goes with it... Because FINALLY Dex gets the courage to FACE his faults too... he also takes responsibility for not pursuing Rachel way back all those years ago at the restaurant. The very weekend that Rachel and Dex cheated on Darcy, Darcy TOO cheated with Marcus! Basically, Darcy was holding on to Dex just to be the upper hand between her and Rachel.... ( Though it was not consciously)... Like I said... It is complex and you will only love this movie if you can relate somehow to these characters.... When Darcy says "I hate you..." It's more than just losing her best friend... It's about losing to Rachel.( Best friend is secondary)....