Some fanfic writers might explore the idea of Ginny having her own hidden motives or desires that conflict with Harry's goals. For instance, she could have a thirst for power that she believes Harry is standing in the way of. Or perhaps she falls in love with someone else and in order to protect that new relationship, she betrays Harry. This would be a very different take on her character compared to the original series, but fanfic allows for such creative reinterpretations.
In some fanfics, it might be for the sake of a more complex plot. The writer wants to create drama and conflict. So, Ginny could be made to betray Harry to add a new layer of struggle to Harry's life. It could also be related to her family loyalty. If the Weasley family was somehow forced into a difficult situation where they had to choose between Harry and their own safety, Ginny might be written to make a choice that seems like a betrayal to Harry.
One possible reason could be a misunderstanding. Maybe Ginny is under the influence of a powerful dark magic that makes her act against Harry without her full control. For example, a powerful mind - controlling spell could be involved.
He could be initially shocked. Harry, who has trusted Ginny deeply, would find it hard to believe at first. He might go through a period of denial, trying to find excuses for Ginny's actions.
One possible reason could be that Harry is too focused on his fight against Voldemort and doesn't want to put Ginny in danger. He might think that being with her would make her a target for his enemies.
Maybe they were forced into it by some dark magic or a powerful dark wizard. They could have been blackmailed into betraying Harry to save their own lives or the lives of others they cared about.
Maybe in the fanfic, Harry discovers some differences between him and Ginny that he hadn't noticed before. For example, their future plans might not align. Ginny might want a more settled life at Hogwarts or in the wizarding community, while Harry feels an urge to explore the wider magical world and perhaps even try to improve relations with non - magical communities. These differences could lead to their break - up.
Maybe in the fanfic, Ginny discovers that Harry has some unresolved trauma from his past, like his experiences with Voldemort. His nightmares and mood swings start to affect their relationship. Harry, on the other hand, might feel that Ginny is too overbearing in trying to 'fix' him. This clash of their approaches to dealing with his past could be a reason for the divorce.
Well, it could be that Harry is secretly in love with Ginny in the fanfic. He might be too shy to express his feelings directly, so he just stares at her, trying to understand her better or just enjoying her presence.
It might be that there was some sort of misunderstanding. For example, a rumor spread that Harry was getting too close to one of his female colleagues at work. Ginny, being a fiery character, got mad without really knowing the truth. In fanfic, these kinds of misunderstandings are often used to create drama.
It could be due to jealousy. Perhaps Ginny has been spending a lot of time with another character, and Harry misinterprets their relationship, leading to his anger. In fanfiction, the writers often play with such emotions to create drama.
Maybe in fanfiction, Ginny discovers that Harry still has some unresolved feelings for Hermione. This could create a rift between them and lead to a divorce. It's not uncommon in fan - created stories to explore complex love triangles that were not fully resolved in the original series.