When Jack returns to school in January, all the boys ignore him. Even kids like Amos and Tristan are short with him, and Jack realizes he has some form of the Plague. The girls all talk to Jack, and the two Maxes say hi, which makes Jack feel bad for never talking to them. At lunch, Jack sits down at his normal table, but all his tablemates get their lunches and move tables to sit closer to Julian. Jack feels awful sitting by himself, so he goes and reads in the library.
Now that Jack seems to be at the bottom of the social hierarchy, he's better able to evaluate his own past behavior and figure out where he could've done better. This shows again how the toxic social structure can keep people from being as kind and as friendly as they could be.