Maybe it's because of their different outlooks on life in the wizarding world. Hermione is very much about following the rules and using magic for good and knowledge, while Draco has been more influenced by the power - hungry and sometimes underhanded ways of his family. This could lead to constant arguments and ultimately a break - up.
It could be due to external forces at Hogwarts. Their relationship might be frowned upon by other students, especially those from the pure - blood supremacist groups. The constant social pressure and possible bullying from peers could make Draco decide that it's not worth it to continue the relationship.
One possible reason could be their different career paths. Harry might be more focused on Auror work which is dangerous, and Hermione, being the practical person she is, may not want to live in constant fear for his safety. Another reason could be a growing apart in their values. Maybe as they get older, Hermione realizes that Harry has a more impulsive nature when it comes to making decisions regarding the wizarding world's politics, while she prefers a more calculated approach.
In the fanfiction, perhaps there are trust issues. Ron has a bit of a jealous streak. If he wrongly accuses Hermione of being too friendly with other male characters, like Harry or some new acquaintance, it could create a rift. This constant suspicion would wear Hermione down, and she might decide she's had enough.
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.
One possible plot reason could be a misunderstanding. Maybe Draco thinks Hermione has some information that she's not sharing and he ties her up to force her to talk. In some fanfictions, it could be part of a game or a dare within the magical world they inhabit. Another reason might be that Draco is being influenced by some dark magic or a curse that makes him act out of character and tie Hermione up.
She might be heartbroken at first. Hermione is someone who invests deeply in her relationships. She would likely retreat into her studies as a way to cope, burying herself in books to try and forget the pain.
One possible reason could be Sasuke's continued obsession with revenge. His single - minded pursuit of power and vengeance might make Sakura feel neglected and unloved in the relationship. For example, he often goes off on long and dangerous missions alone, leaving Sakura behind worried sick. Another reason could be a fundamental difference in their values. Sakura values life and healing, while Sasuke has been more focused on destruction in his quest for revenge.
Jealousy could be another factor. Arthur might be jealous of Merlin's magic or the attention Merlin gets from others because of it. This could create tension and ultimately result in a break - up in the fanfiction.
One possible reason could be miscommunication. Maybe they didn't understand each other's feelings and needs clearly. For example, Harry's preoccupation with his fight against Voldemort might have made Cho feel neglected.
One possible reason could be miscommunication. Maybe Hinata felt that Naruto was always so focused on his ninja duties and didn't have enough time for her. Another reason might be external pressure. For example, if there were some political or family issues in the Hidden Leaf Village that made their relationship difficult to maintain. It could also be that Hinata's own insecurities got the best of her. She might have felt that she wasn't good enough for Naruto, who was a hero in the village.
One possible reason could be that Naruto realizes their goals and values are too different. Naruto is highly focused on protecting the village and achieving peace on a large scale, while Sakura might be more concerned with her medical career and the well - being of a smaller circle. Another reason could be the presence of Hinata. Naruto might gradually develop deeper feelings for Hinata which could lead to the break - up with Sakura.