Maybe there was a betrayal of trust. In the fanfic, Ron could have done something that made Hermione feel she can no longer rely on him. Like he might have shared one of her secrets without permission or made a decision that directly affected her without consulting her first.
One possible reason could be a growing difference in their life goals. Hermione is highly ambitious and focused on her studies and making a difference in the wizarding world. If Ron is more laid - back and not as driven in the fanfic, it might lead to Hermione walking away. For example, she might be constantly frustrated with his lack of initiative in certain important matters.
She becomes more independent. Without Ron by her side, Hermione has to rely solely on herself. This forces her to be more assertive in her decision - making and less likely to compromise her own beliefs for the sake of someone else. For instance, she may be more willing to take risks in her academic pursuits or in her fight for social justice in the wizarding world.
Maybe they run away because they are tired of the constant danger at Hogwarts. They've faced so many threats, and they just want a break. So they run to a peaceful place where no one knows them.
Maybe in the fanfic, Ron's laziness becomes more pronounced over time. Hermione is highly ambitious and hard - working, and she might find Ron's lack of drive frustrating, making her regret her choice.
Well, it could be related to Ron's insecurities. He might be insecure about his place in the group with Harry and Hermione. Hermione is always so confident and sure of herself, and Ron might feel that he doesn't measure up. This could translate into aggression as a way of lashing out. Also, perhaps there's some external influence, like a dark magic object that's affecting Ron's mood and behavior towards Hermione.
One possible reason could be that Hermione wants to pursue her own independent magical research. She is highly intelligent and may feel the need to focus on her studies without the distractions that come with being close to Harry. Another reason might be a disagreement over some major decision in the wizarding world. For example, if Harry has a different stance on how to deal with the remaining Death Eaters or how to reform Hogwarts' curriculum, Hermione, with her strong opinions, may choose to distance herself to avoid constant conflict.
One possible reason could be a conflict of values. Hermione is a strong advocate for justice and equality among wizards and non - wizards alike. Draco, on the other hand, was brought up in a family with pure - blood supremacist views. Hermione might run away from Draco in a fanfiction if she realizes that his views are unchangeable and they are fundamentally opposed to her own. For example, if Draco makes a derogatory comment about Muggle - borns in front of her, it could be the last straw and she decides to run away.
One reason could be she feels extremely pressured by the high expectations at Hogwarts. Everyone expects her to be perfect in academics and problem - solving. Another might be that she discovers some dark secret within the school that she's afraid of, like a hidden plot by a group of dark wizards among the staff or students. Or she could be running away to protect her friends. If she believes that her presence at Hogwarts endangers Harry and Ron, she might choose to leave to keep them safe.
It could be that they lied to Harry about something really significant. In the wizarding world, trust is built on truth - telling. If they told a big lie, like about the true nature of a magical object that was putting Harry in danger, he would be very angry. And if their actions led to the death of someone Harry cared about. For instance, if they made a wrong move during a fight that caused an ally to die, Harry would find it very hard to forgive them.
In some Dramione fanfictions, Ron might break up with Hermione because he feels overshadowed by her intelligence. He could be tired of always being in her shadow and decides to end the relationship. This then paves the way for a potential Dramione relationship as Hermione and Draco start to interact more.
Perhaps in the fanfiction, Hermione leaves Ron because of his jealousy issues. Ron has shown bouts of jealousy in the original series, and if that continued to be a problem in the fan - created story, it could be a major factor. For example, if Hermione started to gain more recognition in the wizarding community for her intelligence and contributions, and Ron couldn't handle it well. Or it could be that new characters were introduced in the fanfiction, and Hermione developed a stronger connection or friendship with them, which made her re - evaluate her relationship with Ron.