Another possibility is that he discovers some dark secrets about his family or his past. These secrets could shatter his perception of himself and his loved ones. It could make him question everything he has known and believed in. For instance, if he finds out that his father was involved in some immoral deeds in the past, it would be a huge blow to him and result in his sadness.
Well, perhaps in the fanfiction, the Order made decisions without consulting Harry. They might have put him in a dangerous situation without his knowledge, like sending him on a mission that seemed suicidal. It could also be that they were keeping secrets from him that he felt were important to his fight against Voldemort.
One possible reason could be differences in their personalities. Harry is often portrayed as more down - to - earth and Fleur as more haughty in the books. In fanfiction, this might be exaggerated, causing her to reject him. Maybe she doesn't like his fame either, as Harry is 'the Boy Who Lived' and always in the spotlight, which she might find tiresome.
In fanfiction, Harry Potter might be angry if his friends are in danger and no one seems to be taking it seriously. He's very protective of his friends, like Ron and Hermione. So if some authority figures in the story are being dismissive of the threats his friends face, that would surely make him angry.
Love could also play a role. Maybe one of the Weasleys falls in love with someone who has a vendetta against Harry. To please their love interest, they could end up betraying Harry. It's a more emotional and complex reason compared to the others, but it can add depth to the fanfiction story.
One reason could be a misunderstanding. Maybe Hermione does something that Harry misinterprets, like getting too involved with her studies and seeming to neglect their friendship. Another could be outside influence. For example, if there are other characters who spread false rumors about Hermione to Harry, it might drive a wedge between them. Or perhaps Harry starts to develop different values and beliefs that clash with Hermione's, leading to a breakdown in their friendship.
In some fanfictions, it could be due to a misunderstanding. Maybe someone framed Harry for a serious rule violation that Gryffindor's house values highly, like cheating in an important magical exam. And the evidence against him seems so strong that the Gryffindor house decides to banish him.
One possible reason could be jealousy. Maybe Harry has some special abilities or has received more attention than his mates, which makes them envious. Another reason might be a misunderstanding. Harry could have been misinterpreted by his mates due to some miscommunication or false rumors.
Perhaps there has been a misunderstanding. Maybe Harry did something that was misinterpreted by his mates, leading to their neglect.
Another reason might be related to his family. In some fanfictions, his parents' story or his relationship with his family members could be distorted. Harry has a strong connection to his family, especially his parents, and any wrong portrayal of that could make him pissed off.
Well, it could also be that Bellatrix is simply bored with the reality of her world in the Death Eater realm. Fanfiction provides an escape into a different world where she can interact with Harry in ways that she may not be able to in the official story. It gives her a chance to be part of new and exciting (to her) adventures that revolve around Harry, even if they are just fictional interpretations created by fans.