The concept of choosing between the "perfect boyfriend" and the "guy she thinks she hates but really loves" isn't groundbreaking, but the story was very well written (especially considering the author was only 18 at the time). Bianca is the 3rd wheel who just goes along with her friends to save them from screwing up. Wesley is a total sleaze who calls her a DUFF and says that speaking to her will increase the chances that one of her friends will sleep with him. She responds with a Cherry Coke to the face. The next time they meet she spontaneously kisses him before then slapping him. From there, he becomes a sexual outlet for relieving the frustrations in her life (parents divorcing and Dad falling off the wagon). They're secretly sleeping together almost daily, but Bianca tells herself it can't grow into anything more than a stealthy "benefits" relationship because she is only a DUFF and Wesley sleeps with any girl that has a pulse. You can probably figure how things work out in the end.
I didn't really enjoy her willingness to be so self-deprecating, but as the story unfolded it made more sense why she was so lacking in confidence. When she was 14 she was having sex with an 18 year old who kept the relationship quiet (until his girlfriend found out and threatened Bianca). She got badly hurt by this guy using her (not to mention the fact that it was statutory rape). Now he's back in town, so she gets herself into the same kind of relationship with Wesley to help numb her, and rationalizes that it's the best she'll be able to do because DUFFs don't get storybook endings.