One possible reason could be ideological differences. Maybe she discovers some practices within the Order that go against her moral compass. For example, if the Order starts to use unethical magic in their fight against the dark forces, Hermione, with her strong sense of right and wrong, might not be able to tolerate it and decide to leave.
Another reason could be personal safety concerns. If she feels that the Order is not doing enough to protect its members, especially after a series of close calls or attacks. She might think that staying with the Order is putting herself and her loved ones at too much risk, so she chooses to leave.
Perhaps she has a new mission or calling that takes her away from Camelot. It could be something related to the greater magical world. For example, there could be an ancient magic that is in danger of being lost or misused, and she is the only one who can save it. Since Camelot has been rather unkind to magic in general, she might feel that she has to leave to fulfill this important task.
It might be due to a self - sacrificing decision on Harry's part. He could believe that by leaving, he would protect the Weasleys from the dark forces that are constantly after him. Since he has so many enemies, he might think that as long as he is around the Weasleys, they are in danger.
One possible reason could be a difference in ideology. Maybe Peter Parker feels that Stark's methods are too extreme or not in line with his own moral compass. For example, Stark might be involved in some projects that Peter doesn't agree with, such as using certain unethical technologies in the pursuit of justice.
One possible reason could be a misunderstanding with his friends in Gryffindor. Maybe there was a big argument over something like a Quidditch match strategy that made him feel alienated.
One reason could be that he feels ostracized. Despite his efforts to protect Konoha, some villagers still look at him with suspicion because of the Nine - Tails inside him. He might just get tired of constantly having to prove himself and decide to leave in search of a place where he can be accepted for who he is.
One possible reason could be that the fanfiction deviated too much from the original character traits of Hermione. Fanfiction often takes creative liberties, and if it strays far from what makes Hermione who she is in the original series, it might make her seem out of character, leading to a decision to leave.
One possible reason could be to escape the danger in England. Given the dark forces that were at play, especially Voldemort's rise, they might have felt it was safer to leave. Another reason could be for a fresh start. Maybe they wanted to explore new magical cultures and communities in other parts of the world.
One possible reason could be a difference in ideology. Maybe Spider - Man has a more local - friendly approach to crime - fighting while the Avengers are often involved in large - scale, global threats. He might feel that his skills are better utilized in his own neighborhood, like Queens, rather than in the grand, often cosmos - level battles of the Avengers.
One possible reason could be a misunderstanding. Maybe they misinterpreted something Hermione said or did, and in a fit of anger or confusion, they decided to leave. For example, if Hermione was working on a project alone without consulting them, they might have felt left out and left in a huff.
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.