Well, it could be that as time passes in the fanfiction world, Hermione witnesses Harry facing great challenges alone. She might feel guilty for not being by his side and regret her rejection. Also, perhaps she starts to have deeper feelings for Harry that she didn't recognize before, like seeing his bravery in a new light and wishing she hadn't turned him down.
Hermione's regret would likely create a lot of tension at first. Harry may be confused or even a bit resentful. But as time goes on, it could lead to a more complex and interesting relationship. Hermione might be more open about her feelings, which could make Harry re - evaluate his own feelings towards her. And this would completely change the way they interact with each other compared to before her regret.
It could be that she sees the pain she caused Harry and it makes her feel guilty. In the story, perhaps she was influenced by others' opinions of Harry and didn't trust her own long - standing friendship with him. When she finally comes to her senses, she regrets all the hurtful things she said or did.
Another reason could be a rift in their friendship caused by outside factors. For instance, if the wizarding community starts to turn against Harry because of false rumors or misinformation, Hermione might find it too difficult to stand by him. She may fear for her own reputation or safety, and this could lead to her abandoning Harry.
In some fanfictions, there might be a new magical element or prophecy that makes Harry question Hermione's motives. If the prophecy says something about Hermione being involved in a dark plot, even if it's false, Harry may start to have doubts about her.
He might regret it because he finally understands that Hermione was the one who truly accepted him for who he was. In fanfiction, often there's a development where characters see beyond the surface. Draco, being from a family with certain expectations, may have found in Hermione someone who didn't care about his family's dark past or his initial snobbishness. When he cheats, he breaks that bond of acceptance, and then realizes how special it was. Additionally, he could be regretful because he sees Hermione move on and be happy without him, and he misses the relationship they had.
Perhaps Harry was seen spending a lot of time with a new character, a girl who was really good at magic and Hermione suspected that Harry was getting some sort of unfair help from her in terms of academics. It could also be that there were some rumors going around in Hogwarts about Harry having an unfair advantage, and Hermione, being the stickler for rules and fairness, immediately jumped to the conclusion of cheating.
In fanfiction, Hermione might choose Ron because he represents a more 'normal' life within the wizarding world compared to Harry. Harry was always the 'Chosen One' with a great burden. Ron, on the other hand, was just an ordinary wizard with an ordinary family (despite its quirks). Hermione might have wanted a relationship that was less centered around saving the world and more about day - to - day life at Hogwarts and beyond.
In the fanfic, Hermione might regret choosing Ron over Harry because Harry has a different level of understanding when it comes to her academic pursuits. Harry, having faced the challenges of fighting Voldemort from a young age, might have a deeper respect for Hermione's thirst for knowledge and her need to constantly learn and improve. Ron, on the other hand, sometimes showed impatience with Hermione's studious nature.
One reason could be jealousy. Maybe Hermione is getting more attention in school for her academic achievements, and Harry, feeling overshadowed, acts mean. For example, in some fanfictions, he might make snide remarks about her always having her nose in a book.
One possible reason could be a misinterpretation of their relationships. Maybe the author wants to explore a different dynamic where Harry and Hermione bond over Ron's perceived flaws, like his occasional laziness or his insecurities that might come across as annoying to them in this fictional scenario.