Perhaps in this fanfiction, Jane has her own personal growth and development that leads her to choose a different path. She might discover new interests or a new sense of self - worth that makes her not want to marry Bingley as she might feel it's not the best fit for her future.
One possible reason could be misunderstandings. Maybe some false information is spread about either Jane or Bingley that creates a rift between them. For example, Bingley might be led to believe that Jane is not truly interested in him.
Well, it could start with a small incident that sets off a chain of events leading to their separation. For instance, Bingley might miss an important event in Jane's life, causing her to feel neglected.
One possible reason could be miscommunication. Maybe there were misunderstandings between Bingley and Jane that led to a breakdown in their relationship. For example, if Bingley misinterpreted Jane's shyness as disinterest.
The plot might develop with Jane being heartbroken at first. She could withdraw from society for a while to deal with her pain. Meanwhile, Bingley may start to realize his mistake as he sees Jane from afar and notices how much he still cares for her.
Naruto could be tired of the expectations placed on him. Everyone has always assumed he would be Hokage since he was a child. He might want to break free from those expectations and define his own path. He may feel that being Hokage is more about fulfilling others' wishes for him rather than his own true desires. So, he decides he doesn't want to be Hokage in this fanfiction.
One reason could be to protect the person he marries. If she's a commoner, for example, the noble society in Camelot might not accept their relationship. So, they keep it a secret. Another reason could be that the person he marries has some sort of power or identity that could put them in danger if it was known. For instance, if she was a sorceress, in Camelot where magic is feared, they'd have to marry secretly.
One possible reason could be that Naruto has been mistreated by the villagers in Konoha for a long time. Despite his efforts to gain acceptance, if he's constantly faced with rejection or unfair treatment, it might lead to him not caring. For example, when he was a child, many villagers shunned him because he was the host of the Nine - Tails. This continuous negative experience could build up over time and cause him to lose his sense of loyalty to Konoha.
In some fanfictions, it could be due to a prophecy or a magical bond that they discover. They might feel that the only way to fulfill the prophecy or strengthen the bond is by getting married secretly. Another aspect could be the political situation in the wizarding world. There could be political factions that would oppose their union for various reasons, such as Harry being seen as a symbol of a certain side and Fleur being from a different background. So, to avoid political turmoil or to keep their relationship safe from political manipulation, they choose to marry secretly.
One possible reason could be that in the fanfiction, Hermione has different career aspirations. She might be so focused on her magical research or her work in the Ministry that she feels marriage would hold her back. For example, she could be on the verge of a major discovery in the field of spell - modification and doesn't want any distractions.
One possible reason could be that he has been living a life apart from his family for so long that he feels alienated. He grew up alone in Konoha, with no knowledge of his family for a large part of his life. So, when suddenly faced with this family in the fanfiction, it's hard for him to accept.
One possible reason could be that Mary Jane has different life goals. Maybe she wants to focus on her career and she sees Peter as a distraction. For example, if she is aiming for a high - profile job in journalism or acting, she might think that a relationship with Peter would take too much time and energy.