Why do a lot of girls like Something Borrowed?

I found out about the movie and novel after watching a spoof of it using Glee characters on tumblr. I have to say after reading the reviews, saving me from watching a Godawful movie (but maybe I'll read the book), I can honestly say why would anyone root for a horrible, backstabbing, jealous "best friend" who wants your life and fiance. She makes Scarlett O'Hara seem like a saint. I didn't like Rachel and I didn't like Dex. Dex was a coward who wanted his cake and eat it too. I will never understand why people stay with someone they're cheating on. Maybe the author wasn't glorifying cheating and wanted to make the characters deplorable, but I can't enjoy a book were a ***** is made to be the good guy. I think I like Darcy because even though she was a snob and kind of an assertive person who took advantaged of people, that didn't make her a bad person. She had her moments, but that doesn't excuse Rachel's actions. Darcy did cheat, okay. But why did the guy throw it in her face to make himself look better. I'll tell you why. Because he thought he was enjoying cheating on his "faithful" fiance with her best friend and lost his "machoness" and "pride" when he found out Darcy pulled a Miranda Lambert.