In some fanfictions, Dumbledore might be portrayed as betraying Harry by withholding crucial information. For example, if he knew more about Harry's fate or the true nature of the threats he faced but didn't share it all. This could make Harry feel betrayed as he was left in the dark and had to face greater danger without full knowledge.
A common scenario is when Dumbledore lies about Harry's family history. If he hid important details about Harry's parents or their relationship with certain dark forces, Harry would feel betrayed. Another could be Dumbledore giving Harry tasks that were actually much more dangerous than he let on, like sending him into a trap unknowingly.
In certain fanfictions, Dumbledore's secrets are the root of the perceived betrayal. For instance, his secrets about the Deathly Hallows. If Harry discovers that Dumbledore had known more about the Hallows all along and didn't share this knowledge, which could have changed Harry's journey and decisions, it could be written as a betrayal. Harry may feel that he was used and misled by Dumbledore, and thus the idea of betrayal emerges in these fan - created stories.
A common plot is that Dumbledore has been manipulating Harry from the start. He might have arranged events in Harry's life to lead him to a specific fate against Harry's will. For example, making sure Harry attended Hogwarts to be part of the fight against Voldemort.
Dumbledore might be motivated by his over - arching plan to defeat Voldemort. He could see Hermione as a sacrifice that needs to be made. Maybe he believes that by betraying her, he can gain some crucial information from the enemy that will ultimately lead to Voldemort's downfall.
One way it could develop is if Dumbledore withholds important information from Hermione about her family or her own magical abilities. He might do this because he fears she will use that knowledge in a way that could disrupt his grand plan for the wizarding world. For instance, Hermione discovers she has a special power that could defeat Voldemort easily, but Dumbledore has kept it from her all along, making her feel extremely betrayed as she could have saved many lives if she knew earlier.
Dumbledore, as Harry's guardian in the fanfiction, would probably use his influence in the wizarding world. He could make sure that Harry is taught by the best teachers at Hogwarts. He'd also be there to offer advice and guidance, especially when Harry faces challenges like dealing with Voldemort or other dark forces. For example, he might teach Harry some advanced defensive magic privately to better protect himself.
Well, in some fanfictions, Harry might attack Dumbledore if he discovers that Dumbledore has been using him as a pawn in a bigger game all along. This feeling of betrayal could drive him to lash out. Also, if there is a prophecy that he misinterprets to mean Dumbledore is a threat to his future or the future of his friends, that could be a motive.
Snape can be a prominent character. Given his complex relationship with Dumbledore and Harry, his perspective could add a lot to the story. He might have some insights into Dumbledore's actions that Harry doesn't know about, and his reactions to Harry's blaming could vary from being scornful to having a moment of understanding. Luna Lovegood could also be a part of it. Her unique view of the world might make her offer some different viewpoints on the situation between Harry and Dumbledore.
Well, it could be many reasons. Maybe there was a misunderstanding. Some dark magic might have been used to make his friends think he did something bad. Or perhaps a powerful enemy framed him by planting false evidence. It's hard to say exactly without more context from the fanfiction.