It could be due to a misunderstanding that got out of hand. Ron and Hermione might have been involved in something that Harry misinterpreted as a sign of their disloyalty. For instance, they were secretly working on a project that Harry thought was against him, but in reality, it was for his own protection. However, because of the lack of communication, Harry's anger and unwillingness to forgive grew.
It could also be due to a long - standing pattern of behavior. If Ron had been constantly critical or undermining of Harry in the fanfiction, Harry might reach a point where he just can't forgive. Say Ron always made fun of Harry's decisions in front of others, which gradually eroded Harry's trust and patience.
One possible reason could be a major betrayal. Maybe Hermione made a decision that seriously endangered Harry's life or the lives of their friends, like revealing a crucial secret to the enemy. This would be a huge breach of trust and could lead to Harry not forgiving her.
One reason could be that Ron abandons Harry when he needs him the most. Like in a dangerous situation, if Ron runs away leaving Harry alone to face the threat, Harry would find it hard to forgive such cowardice.
Well, it could be that in the fanfiction, Ron made a mistake that had long - lasting consequences for Harry. Maybe Ron accidentally revealed one of Harry's big secrets that put Harry in danger. So, Harry is unable to forgive Ron as it has changed his life in a negative way.
Perhaps there were some secrets that Ron was keeping from Harry. In the wizarding world, secrets can be a big deal. If Ron had a secret related to his family or some other important matter and Harry found out about it in a way that made it seem like Ron was hiding something bad, it could lead to Harry not trusting him. Also, Ron's friendship with other characters might make Harry jealous or suspicious. If Ron was getting closer to someone Harry didn't trust, it could spill over and make Harry question Ron's loyalty to him.
It could also be due to a series of unlucky events. Suppose Hermione's well - intentioned plans keep backfiring in a way that makes Harry question her judgment. Like when she tries to solve a problem but ends up making it worse, Harry might start to lose trust.
It could create a rift in the Order of the Phoenix. Since the three of them were important members, their conflict might split the group into factions. Some might side with Harry, believing he has a right to be angry, while others might think Ron and Hermione should be given a chance to explain. This division could weaken the Order's ability to fight against Voldemort.
One possible reason could be miscommunication. Maybe Ron said something that Harry misinterpreted, leading to the distrust. For example, if Ron made a joke about Harry's abilities in a time of stress, Harry might take it the wrong way.
It could be due to a misunderstanding. Suppose Ron overhears a conversation between Harry and Hermione that he misinterprets completely. He might think they are plotting against him or don't really consider him a true friend. So in a fit of anger and hurt, he decides to betray them.
Perhaps in this fanfiction, Ron's loyalty is in question. Harry and Hermione value loyalty highly, and if for some reason Ron is portrayed as being unfaithful or unreliable in the story, it could cause them to dislike him. For example, if he were to side with someone against Harry and Hermione's best interests, that would be a big factor.