- The casting of Blake Lively and Justin Baldoni as Lily and Ryle caused backlash from fans because in the book Lily is 23 and Ryle is 30, while Lively is 35 and Baldoni is 39. Author of the book Colleen Hoover explained in an interview that she wanted to age the characters up in the movie in an effort to correct a mistake she made in the book. She said, "Back when I wrote It Ends With Us, the new adult [genre] was very popular. You were writing college-age characters. That's what I was contracted to do. I made Lily very young. I didn't know that neurosurgeons went to school for 6-12 years. There's not a 20-something neurosurgeon. As I started making this movie, I'm like, 'We need to age them out, because I messed up.' So, that's my fault."
- The song Britney Spears: Everytime (2004) is featured in the movie, with Britney Spears being thanked in the ending credits. Blake Lively is a big fan of Spears and also paid homage to her in the premiere of the film by wearing a vintage Versace dress that Britney herself wore in 2002 to a Versace fashion show.
- While the film is based in Boston, it was filmed in New Jersey, primarily in Hoboken and Jersey City.
- This film opened at #2 at the box office after Deadpool & Wolverine (2024), starring Blake Lively's husband Ryan Reynolds (coincidentally, Rob Simonsen also scored both films). This made Reynolds and Lively the first married couple to star in the top two films at the box office since Bruce Willis and Demi Moore in 1990, when Ghost (1990) opened at #2 after Die Hard 2 (1990), but gained the #1 spot the following week.
- Blake Lively's sister Robyn Lively & Justin Baldoni's wife Emily Baldoni have small roles in this film.
- Despite being the two main stars of the film, Justin Baldoni and Blake Lively didn't do any promo for it together nor they took photos together in its premiere. There are rumors both clashed due to creative differences in the making of the movie.
- Colleen Hoover makes a cameo at Alyssa's birthday party scene. She's shown briefly and then she can be seen again in the background.
- At the movie's premiere, Entertainment Tonight asked Baldoni if he was willing to direct and star in a sequel based on Hoover's follow-up book, It Starts with Us. Baldoni immediately suggested the perfect candidate to take over the directing job: "I think there are better people for that one," he said. "I think Blake Lively is ready to direct."
- Ellen DeGeneres is a key aspect of the book that is not carried over to the film. However, we do briefly see Ellen on TV at one point. We also see a Finding Nemo poster on young Lily's bedroom wall, and a Nemo stuffed toy in the nursery. Ellen, of course, plays Dory in Finding Nemo.
- The name of Atlas's restaurant has been changed. In the book it is BIBs (short for "Better in Boston") but in the movie it's been changed to "Root".
- Blake Lively confessed during the premiere that her husband Ryan Reynolds wrote/created a very pivotal scene in this movie. Lively confessing this was controversial, since he wrote the scene during the WGA writer's strike, when nobody (including actors as they're a part of the SAG-AFTRA union) was allowed to write, meaning that he broke solidarity with the actors when he wrote the scene.
- Based on the New York Times Best Seller "It Ends With Us" by Colleen Hoover.
- There are two cuts for this movie: one commissioned by producer Blake Lively, from editor Shane Reid, who was also an editor on her husband Ryan Reynolds' latest movie, "Deadpool & Wolverine"; and the other by director Justin Baldoni, from editors Oona Flaherty and Robb Sullivan - who were ultimately credited. It's unclear which was used in the final project, but it is said that the team was in agreement on the final cut.
- Actress and activist Alexa Nikolas lambasted the soundtrack on Instagram for featuring a song by her abusive ex-husband Michael Milosh, founder and singer of the band Rhye.
- Grace Caroline Currey, Daisy Edgar-Jones, Virginia Gardner, Lucy Hale, Danielle Macdonald, Florence Pugh, Lili Reinhart, Margot Robbie, Saoirse Ronan, and Anya Taylor-Joy were considered for the role of Allysa, which went to Jenny Slate.
- Kevin McKidd also played a physically violent husband in Rome (2005).
- Many of the clothes worn by Lily are actually from Blake Lively's own wardrobe, such as the Saint Laurent sparkly fishnet mesh pointed-toe boots.
- The title is spoken by a character at almost the end of the film.
- While decorating the flower shop, Lily Bloom (Blake Lively) can be seen hanging an emptied hornet's nest. The actress was unaware that it used to be real.
- This is the second film in August of 2024 to feature a character named Atlas, the first being Borderlands (2024). Both films were released on August 9th.
| Spoiler Warning: The following contains important plot details of the entire film. |
- Pivotal book scenes that didn't make the final cut: Poker night/Cassie never existed & Lily's mom knows that she chose not to speak at her father's funeral and has never felt prouder of her.
| Spoiler Warning: All spoilers have been stated and have ended here. |