I'm not sure specifically if there is a fanfiction titled exactly like that, but in the Harry Potter fanfiction community, all kinds of relationship - based plot twists are explored. It could be that someone has written a story where Cho cheats on Harry. You can try searching on popular fanfiction websites like Archive of Our Own or FanFiction.net to find out.
In this fanfiction about the Yule Ball, there are many possibilities for Harry and Cho. They could be initially hesitant around each other. However, the Yule Ball is a special event full of magic and wonder. Maybe they find a quiet corner to talk, away from the noise and the crowd. During their conversation, Cho might open up about her feelings for Cedric, which could lead to Harry comforting her in a new and deeper way, strengthening their bond.
Hermione Granger could be one of the characters. Since she is Harry's close friend, it would be interesting to see how she fits into the harem dynamic, whether she's supportive or has some mixed feelings about it.
Harry is the most important character interacting with Yandere Cho. But we can't forget about Luna Lovegood. Luna might notice Cho's abnormal behavior and try to warn Harry. Also, Cedric Diggory's memory could play a role. Since Cho was Cedric's girlfriend before, his memory might haunt her and fuel her yandere tendencies, and this could be noticed by characters like Harry when they interact with her.
Hermione could be one of the main characters. She might be the one who encourages Harry to stand up to Cho Chang if she thinks Cho Chang is treating Harry unfairly. Or she could be there to mediate the situation after Harry tells Cho Chang off.
Cho's comfort can make Harry more open. Usually, Harry is quite reserved about his feelings. But when Cho comforts him, he starts to share more. For example, he might open up about his fears regarding Voldemort.
One common theme is unrequited love. In many fanfictions, Cho's feelings for Harry are often more intense than he initially realizes. Another theme is dealing with grief. Given their experiences in the wizarding world, they often have to cope with the loss of friends together.
No. In general, fanfics should promote positive values or at least be within the boundaries of acceptable behavior. This kind of description involves physical harm in a very private and painful area, which goes against the norms of what is considered proper in most forms of literature, especially fan - based works that are often read by a wide range of ages.