So...how did Lance figure it out??

Been awhile since I watched but want to say due to the girl in the book was known as the gf to the athlete guy, so he first knew those two characters could have been him and Mia but he blew it off as chance. Then as he kept reading the book he read how the gf character got close to that of Harpers character and how Harpers character kissed her on the forehead. Which Lance knew was a signature of Harpers ~ letting him then to realize that the book was actually based on them.


Poop in his hand ... Poop in his hand

Also, Harper kept taking Lance's copy of the book, leading Lance to wonder what is up.

Cause Lance knows Harper inside-out. He knows Harper back in the day was as much of a playa as him, and he knew how close him and Mia were. Harper never came out and admitted in the book that they slept together, but Lance knew Harper well enough to know they didn't just cuddle and that was the end. Plus, like someone else said, Harper had been trying to keep the book from Lance, and that alone was a sign a secret was in the book.

I think it's a combination of things.

In the book, Mia's character and Harper's character do nothing but cuddle, sleep in the same bed together, and he kisses her on the forehead. Jordan's character and Harper's character have crazy sex.

Now, if Harper hadn't put that last bit in, I think if he would have been fine. What gave it away is that everyone knows Jordan and Harper slept in the same bed, cuddled, and kissed. He essentially switched the characters but left the actions the same.

Lance was suspicious because Harper kept trying to steal the book away, but that switcheroo and the forehead kiss is what did it. Jordan explained it all in the store when they were buying Lance and Mia's wedding gift.

When Lance is sitting in the bathroom reading the book, you can see him becoming increasingly agitated because he's seeing how Harper comforted Mia after Lance betrayed her. What seals it is that all Harper's character does is kiss Mia on the forehead. Lance knows exactly what that means.