Perhaps Jacob could start to spread negative rumors about Bella among their mutual friends. This would create a rift not only between them but also within the larger group that they are a part of. He may feel betrayed by Bella for some reason and wants others to see his side.
There could also be other characters from the Twilight series involved. For example, the members of Jacob's wolf pack might play a role. They could be trying to mediate between Jacob and Bella, or they might side with Jacob, adding more tension to the story.
In some fanfiction, Bella might not forgive the Cullens because of a perceived betrayal. For example, if they hid something crucial from her again. It could also be due to them putting her in danger without her consent. Another reason could be a broken promise related to her transformation or her relationship with Edward.
Perhaps in the fanfiction, Edward broke a significant promise to Bella. Promises are important in relationships, and if he failed to keep one, it could lead to her not forgiving him. For example, if he promised to always be there for her but then abandoned her in a time of need. Also, his over - protective nature in a wrong way could make Bella feel suffocated and less likely to forgive him.
In fanfiction, a scenario could be that the Cullens exclude Bella from important family decisions. This makes her feel like an outsider and unloved. Or perhaps they try to manipulate her into doing something she doesn't want to do, such as leaving her human friends behind. This would lead to her not forgiving them.
It can add a new perspective to the fandom. Fans who are tired of the typical Bella - Edward love story might find these fanfictions refreshing. It shows that relationships are complex and not always about happily - ever - after. It can also inspire discussions among fans about the characters' flaws and what could realistically happen in such a relationship.
The plot could develop with Jacob focusing on his own growth and self - discovery. He might leave Forks to explore other werewolf packs or just to be on his own for a while. This would create a distance between him and Bella, and the story could then show how Bella reacts to his new - found independence.
One reason could be that Jacob realizes they have different life goals. Bella is often so focused on Edward and the vampire world, and Jacob may feel that his werewolf life and values are too different from hers to have a romantic connection. For example, he might want a more traditional werewolf life with his pack, while Bella is constantly drawn to the dangerous and alluring vampire lifestyle.
Maybe he doesn't like the way his character is often misinterpreted or distorted in fanfiction. Some fanfictions might take his character in directions that he would find unacceptable or disrespectful.
In some fanfictions, Harry might not forgive McGonagall because she may have made a decision that Harry feels was a great betrayal. For example, if she sided with the Ministry when they were unjustly treating him. It could also be that she failed to protect him or someone he cared about in a crucial moment within the fanfiction's plot.