In the fanfiction, it could be that Harry has been getting too friendly with another witch. Ginny, being possessive and in love with Harry, would not take kindly to this. Also, if Harry didn't support Ginny in one of her personal endeavors, like trying to get a promotion at the Ministry or something related to her writing, she might be angry at him.
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.
Perhaps Harry accidentally revealed one of Ginny's secrets to someone she didn't want to know. Or he made a comment that was unintentionally offensive about her Quidditch skills. Ginny is a strong - willed character, and if she feels disrespected or ignored by Harry, it would make her angry.
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.
One possible reason could be miscommunication. Maybe they had a big fight over how to raise their child and Ginny, feeling unheard, decided to leave. Another reason might be external pressure. For example, if some dark forces were targeting their family again and Ginny thought leaving would keep Harry and the child safer. Or perhaps Ginny had some personal issues she couldn't deal with while being in the family, like feeling she lost her own identity in the relationship.
One possible reason could be the stress of Harry's fame. His status as 'The Boy Who Lived' might put a lot of pressure on their relationship. Constant media attention and public expectations could lead to arguments and a growing distance between them.
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 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.
One possible reason could be a misunderstanding. Maybe Harry was wrongly accused of something, and Ginny's temper got the better of her. For example, if there were false rumors about Harry being unfaithful in the fanfiction world.
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.
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.
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 jealousy. Maybe she sees Harry getting too much attention or having relationships with other characters that make her feel left out and envious, which then turns into hatred and a desire to kill. Another reason might be a misunderstanding. Harry could be involved in some secret mission or activity that Ginny misinterprets as something harmful, leading her to think he's a threat.