One possible reason could be that Harry has seen so much death and destruction during the war that he is afraid of forming new, deep emotional bonds. He might worry that he could lose his loved ones again, so he refuses to marry as a way to protect himself from potential future heartbreak.
The fanfiction might explore Harry's character development by highlighting his independence. Harry has always had a sense of duty, but now he is making a decision for himself, regardless of the potential consequences. His refusal to marry could be a way of asserting his own will and breaking free from the expectations that have been placed on him all his life. This is a significant step in his character's evolution.
She might be heartbroken. Ginny could initially be in shock and disbelief. She may retreat into herself, spending a lot of time alone in her room, crying and trying to understand why Harry would refuse.
Ginny could be heartbroken. She might initially be in denial, thinking that Harry will change his mind. She has loved Harry for a long time and expected a future together, so this refusal would be a huge blow to her emotions.
Ginny could be heartbroken. She might have expected to marry Harry after all they've been through together. She could initially go into a state of shock and disbelief, not understanding why Harry has refused.
One possible plot could be that after the war, Harry and Hermione realize they have a deep bond that goes beyond friendship. They start to rebuild Hogwarts together and in the process, their feelings grow. They get married in a small ceremony at Hogwarts with their closest friends in attendance.
One possible reason could be that Harry is still haunted by his past traumas and feels he's not in the right mental state to marry anyone. His experiences with Voldemort and the losses he's endured might make him reluctant to bring Ginny into a potentially unstable future.
One possible reason could be their fundamental differences in personality. Harry is brave and impulsive at times, while Snape is often brooding and secretive. Their past interactions, which were mostly filled with animosity and mistrust, could also be a factor. Harry might not be able to see Snape in a romantic light due to all the times Snape was cruel to him in school.
Maybe Harry has some unresolved issues from his past, like the trauma of losing his parents and many of his friends during the fight against Voldemort. These could make him hesitant to enter into a marriage with Ginny. He might also be worried about how the wizarding world would view their marriage, especially if there are still some who oppose him or his family.
One possible reason could be that she doesn't see Ron in a romantic way. In the story, perhaps she views Ron more as a brother or a close friend. Their relationship might be based on camaraderie rather than romantic love, so she refuses to marry him.