One reason could be that Cho is still hung up on Cedric. Even though she starts dating Harry, her feelings for Cedric might resurface and lead her to cheat. Another possibility is that she feels pressured in her relationship with Harry due to all the attention they get at Hogwarts and looks for an escape with someone else.
In a fanfiction, it could be that the writer wants to show Cho's character flaws. Maybe she's a bit more self - centered than she seems in the books and cheats on Harry because she meets someone who she thinks can offer her more, like better social status among the students or more exciting adventures. Also, it could be a way to explore Harry's reaction to betrayal and how it would shape his character further.
Well, perhaps in the fanfiction, Cho cheats on Harry because she gets influenced by some dark magic or a charm that makes her act out of character. Or maybe she starts to feel that Harry is too preoccupied with fighting Voldemort and not giving her enough attention. Additionally, it could be that she misinterprets her feelings for Harry as just a passing infatuation and when she meets someone new, she acts on her new - found 'feelings' without thinking clearly about the consequences to her relationship with Harry.
A practical answer is Chapter 15, because it turns the idea into a concrete scene. The chapter opens with Jiang Shixu woke up from those nightmares filled with blood and darkness,..., adds pressure through Jiang Shixu's mind was starting to cloud, but for some reason, when he..., and ends on Since.
The best chapter pointer here is Chapter 20, "Miss Su, your defense is somewhat clumsy". It opens with Several people turned their heads upon hearing the sound and saw three... and closes on So, he turned and questioned Jiang Li..
Chapter 806, "Flip the Table!", is the clearest early answer because it turns Jiang Zhao Yuan's situation into a concrete plot event. Early on, Jiang Li looked at the dining room that seemed to have been hit by a.... By the end, In an instant, the dining room fell silent..
Chapter 825, "This method is absolutely not feasible!", is the clearest early answer because it turns Qixing Tower's situation into a concrete plot event. The chapter turns that into something concrete by moving from Beside him, Yu Qing: "....." Why does it feel like neither of them...
Look to Chapter 15 for the clearest answer. It begins with Jiang Shixu woke up from those nightmares filled with blood and darkness,..., keeps building through The two sleeping pills he took in the evening had left him with a..., and lands on Since she didn't move, Jiang Shixu also stayed put, and.
Chapter 926, "Doomsday Beehive Exploded?!", is the clearest early answer because it turns Yu Fei's situation into a concrete plot event.
If you want the clearest chapter reference, go to Chapter 2. Early on, On the top floor of the Financial Building, a gathering of dark clouds...; later, the chapter leans on How dare Jiang Li hang up his phone?.
The best chapter pointer here is Chapter 21, "Uncle Policeman, They Are the Ones Causing Trouble!". It opens with Jiang Li's clear and logical explanation had everyone stunned in place. and closes on But the implications could be different..
A practical answer is Chapter 379, because it turns the idea into a concrete scene. The chapter opens with Aberdeen City, 1 year prior Inside a high-end hotel room penthouse,..., adds pressure through He rubbed his palm against her cheek and grinned., and ends on His wife gave him a bespoke Swiss.
Chapter 704, "Even if I were a slave, I would be willing!", is the clearest early answer because it turns Bai Lu's situation into a concrete plot event. The chapter gives readers a real answer by opening on Wu Daoshan looked at Zhao Lang in shock.