The Summer I Turned Pretty's third book, We'll Always Have Summer, revealed the main reason why Belly broke up with Jeremiah, and it's pretty unfortunate. The Amazon Prime Video series returns with its final season, continuing Belly's (Lola Tung) journey of self-discovery as she navigates the complexities of her love story with her boyfriend, Jeremiah Fisher (Gavin Casalegno). Season 3 is primarily based on We'll Always Have Summer, meaning that most of what happened to Belly in the book will be adapted on-screen. In fact, Episode 1 already showed a pivotal moment between Belly and Jeremiah: their breakup.
The Summer I Turned Pretty Season 3 Episode 1 ended with Belly finding out about Jeremiah's cheating shenanigans during his spring break trip to Cabo, which ultimately put a nail in their relationship. Interestingly, the same thing happened in the books, dampening Belly and Jeremiah's already-fragile relationship.
The Summer I Turned Pretty features the return of Lola Tung, Gavin Casalegno, Christopher Briney, Sean Kaufman, Rain Spencer, and Jackie Chung. Season 3 premiered on Prime Video on July 16, 2025.
Why Did Jeremiah & Belly Break Up in Summer I Turned Pretty Book 3?
We'll Always Have Summer, the third and final book of The Summer I Turned Pretty series, revealed that Belly and Jeremiah also broke up due to the same reason. It turned out that Jeremiah also slept with a sorority member named Lacie Baron at a fraternity party during spring break.
Jeremiah decided to keep it from Belly because he did not want to lose her. It was a bold move for him to betray an honest and innocent girl like Belly, but it came back to bite him in the end.
At a post-finals party, Belly overheard Lacie and her friends discussing the night Jeremiah slept with Lacie during spring break. Belly confronted Jeremiah, and he told her the truth. However, Jeremiah pointed out that they were on "break" during that time, so it didn't count.
Jeremiah said this in reference to their fight right before spring break, which seemingly ended with them "breaking up." Still, Belly didn't see it that way because she thought it was just a misunderstanding.
Jeremiah saw it otherwise because he believed that they were not together anymore during that moment, so sleeping with Lacie meant no harm. This revelation about Jeremiah's cheating incident ultimately led to their real breakup in the book.
While this cheating fiasco significantly damaged their relationship, the pair eventually got back together after Jeremiah opened up about wanting to never lose Belly again. Jeremiah then proposed to Belly, and she accepted (even though it's clear that she still had lingering feelings for Conrad).
In the series, Jeremiah's proposal also halted Belly's plans to go to Paris for a study-abroad program.
Did Jeremiah Really Love Belly?
There was no doubt that Jeremiah really loved Belly in both the books and the series, but the fact that he did not choose to outright tell her about his hookup with Lacie during spring break should raise some eyebrows about his loyalty to his girlfriend.
Speaking with People, The Summer I Turned Pretty author Jenny Han pointed out that Jeremiah's cheating issue is "debatable" and it's up to fans how they interpret it because "they technically were broken up" at the time:
"[It's] debatable whether or not that's considered cheating or not. Because they technically were broken up. It's really how different people [interpret it]."
Whether he cheated or not, it was clear that Jeremiah hurt Belly's feelings, which essentially made her rethink her love for him. In the book and the series, Belly also kept a secret from Jeremiah after she spent Christmas with Conrad at the Cousins' house (but they did not sleep together, unlike what Jeremiah did).
Still, it was clear that Jeremiah and Belly had unresolved issues. Jeremiah's recklessness showed him as an unreliable partner willing to bail on Belly when the going gets tough. Meanwhile, Belly's lingering feelings for Conrad have yet to be resolved, and it will get tougher if she decides to stay with Jeremiah because she will always wonder about the what-ifs.
All in all, marriage is not a long-term band-aid solution that would miraculously fix them.
