Jeremiah cheated on Belly with a girl named Lacie Barone. This happened during spring break in Cabo while Jeremiah and Belly were on a break, although Belly thought they were just temporarily apart. Belly overheard Lacie talking about hooking up with Jeremiah, which led to Belly confronting Jeremiah and breaking up with him. Jeremiah defended himself by saying they were broken up at the time, making it debatable whether it was technically cheating or not, but it deeply hurt Belly. This incident plays a significant role in their relationship dynamics in both the book series and the TV show "The Summer I Turned Pretty".