Perhaps Harry still has unresolved emotional issues from his past, like the loss of his parents. This could make him feel unworthy of Ginny's love and lead him to reject her. He may also be afraid of commitment and the responsibility that comes with a relationship at that time.
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.
Alternatively, Ginny could be very mature about it. She might respect Harry's decision, even though it hurts. She could choose to step back and give Harry the space he seems to need while secretly hoping that he will change his mind in the future.
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.
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.
One possible reason could be a growing apart due to their different career paths. Harry, being deeply involved in the wizarding world's security and Ginny having her own Quidditch career. Another reason might be the stress of living in the public eye. Their relationship may not be able to withstand the constant scrutiny and pressure from the wizarding community.
Well, it could be that Harry has a different view on how to handle the war against Voldemort. Dumbledore is often very strategic and sometimes keeps things from Harry for what he believes is the greater good. But Harry might think that full transparency is necessary. Also, Harry may have formed new alliances or friendships that give him different perspectives, and these new ideas conflict with Dumbledore's. He might feel that Dumbledore's approach is too old - fashioned or risky in a new context.
One possible reason could be miscommunication. Maybe Ginny feels neglected by Harry because he's so caught up in his own heroic deeds and doesn't pay enough attention to her. So she might seek comfort or excitement elsewhere.
One possible reason could be that Ginny has seen Harry change a great deal during the war. Maybe the war has left Harry with a lot of emotional baggage that he's not dealing with well, and Ginny doesn't know how to handle it. So, she decides to give him some space by ignoring him for a while.
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.
One possible reason could be that he might fear for Ginny's safety. In the wizarding world, there are always threats from dark forces. Harry has already lost many people he loves, and he might not want Ginny to be in more danger because of their relationship. Another reason could be that he wants to focus on his own personal growth and exploration. Harry has spent so much of his life fighting Voldemort and dealing with the wizarding world's problems that he may feel he needs time alone to figure out who he really is without the added pressure of a marriage.
One possible reason could be that Harry has been spending too much time on his heroic duties and not enough time with Ginny. Another might be that he made a decision without consulting her, like taking on a particularly dangerous mission. It could also be something as simple as he forgot an important date or anniversary.