You know those people who start dating someone and become all about that person, to the exclusion of their friends? What's up with that, anyway? The character most likely to shed some light on the phenomenon is Joni, Paul's oldest and dearest friend.
When the story opens, Joni has recently broken up with her boyfriend Ted for the thirteenth time—which, as everybody knows, is the charm. For some inexplicable reason, she hooks up with Chuck, a football player with the IQ and personality of a rock. Speaking of rock, one of Chuck's more inspired and passionate statements is, "Our practices have been so rockin' lately" (9.55).
So why does she go for him? Well, one reason is that he's not Ted. Another is that he treats her badly, complaining when she wants to hang out with her friends. Joni, like so many teenage girls before her, falls into the trap of you're-lowering-my-self-esteem-I-really-want-you-now. (Don't worry, teenage guys who like to date teenage girls; they outgrow it.)
Joni's been Paul's closest companion—some might say appendage—since they were little kids. Their lives are totally intertwined, as the lives of childhood best friends become. But when she gets with Chuck, Joni has a momentary lapse of reason and stops speaking to Paul when he tells her Chuck's kind of a loser.
When Paul begs her to come to Tony's house and help talk his parents into letting him go to the dance, she's not swayed at first, but fortunately she comes to her senses and shows up. She may have to drag Chuck behind her complaining all the way, so hers isn't an entirely happy ending, but it shows she hasn't completely lost her mind.