In both versions, Peter and Lara Jean argue after the tree house party. Both arguments are largely sparked by John Ambrose and Gen, and the jealousy they've both inspired. Shortly after that, Lara Jean finds out that Peter knew the whole time that it was Genevieve that posted the video of them in the hot tub and more importantly, that Genevieve only knew Peter would be there because he was waiting for her... not for Lara Jean. The devastating discovery leads Lara Jean to suggest that maybe she and Peter shouldn’t be together. In the book, the game Assassins largely plays into the building tension and their breakup, especially when Peter makes an alliance in the game with Gen.