In this fanfiction, it might be that Bella has received some sort of premonition. She could have seen a future where staying with the Cullens leads to their destruction. Out of love for them, she chooses to say goodbye. She might plan to go far away, change her identity, and live a life away from the supernatural world that has been both alluring and dangerous for her.
Edward would likely be the most affected. He's in love with Bella. Her leaving would be like losing his whole world. He might become withdrawn and even more brooding than before.
Well, it could be due to the way the Cullens interact with the other people in Forks. If Bella notices that they are being manipulative or using their powers in a way that she doesn't like to influence the townspeople, that could make her start to hate them. Also, if there is some kind of power struggle within the Cullen family that starts to affect Bella negatively, like she gets caught in the middle of it or she sees how it's causing harm to those she cares about, she might turn against them.
Maybe Bella turns out to have a connection to an ancient vampire lineage that has a feud with the Cullens. This would create a lot of tension and conflict as she tries to navigate her feelings for the Cullens while dealing with this newfound connection.
Well, it could involve Bella adjusting to her new life with the Cullens. Maybe she has to learn their unique family rules and deal with the fact that they are vampires. She might also face challenges from other vampires or supernatural beings who don't like the Cullens taking in a human.
It's possible that in the fanfiction, the Cullens are involved in some sort of betrayal. For example, they might side with someone who is against Bella. This act of betrayal would be a strong reason for her to hate them. In fanfiction, new storylines can be created where the Cullens' actions are not in line with what Bella expects or desires, which can result in her hatred.
In some fanfictions, Bella might accidentally harm one of the Cullens, either physically or emotionally. This could lead to them hating her. Also, if she were to side with their enemies in a conflict, that would definitely make them dislike her. For example, if there was a feud between two vampire groups and Bella chose the wrong side, the Cullens would not be happy with her.
In the 'the cullens kidnap bella fanfiction', it could be that the Cullens have some hidden motives. They might believe that Bella has a special power or connection that they need to study or keep safe. So they take her against her will, which then leads to a complex relationship dynamic between Bella and the Cullens as she tries to figure out what they really want.
In the 'bella is kidnapped by the cullens fanfiction', one possibility is that Bella is kidnapped to be part of some vampire ritual. However, she refuses to cooperate at first. The Cullens then have to try and convince her that it's not as bad as it seems. This could involve showing her their more human - like qualities, like their love for art and music. As Bella spends more time with them, she may start to see them in a different light and even develop feelings for one of them.
One possible reason could be that she discovers some dark secrets about the Cullens. Maybe she finds out they have been lying to her about their true nature in a more malicious way than in the original story. Another reason might be that she feels threatened by their vampire powers. If they accidentally or purposefully use their powers around her in a menacing way, it could make her feel scared and turn that fear into hatred.
One possible plot could be that Bella discovers the Cullens are homeless for some reason, perhaps they've been run out of their home by a new vampire threat. Bella then uses her connections in the town and her knowledge of the area to find them a safe place to stay. She might also help them gather resources, like getting blood from a hospital in a discreet way.