Perhaps in the fanfiction, Sakura hurt Naruto's feelings regarding his relationship with Sasuke. Naruto has a deep bond with Sasuke, and if Sakura did something to interfere negatively in their relationship, like trying to force Naruto to give up on Sasuke or saying hurtful things about their friendship, Naruto would likely not forgive her.
It could also be due to Sakura constantly doubting Naruto's abilities in the story. Naruto has always been looked down upon by many in the original series, and if in the fanfiction Sakura continuously expresses her lack of faith in him, it could lead to his unforgiveness. For example, she might have refused to believe in Naruto's new jutsu or his plans to save the village, which made Naruto feel really disappointed and unable to forgive her.
Well, in the fanfiction context, Naruto may not love Sakura because he has unrequited feelings for someone else. Maybe he has a deep connection with another character that makes him view Sakura just as a teammate. Also, their personalities might not be as compatible in a romantic sense as one would initially think. Naruto is often impulsive and headstrong, while Sakura can be a bit more reserved in some ways, and this could lead to a lack of romantic attraction.
In the fanfiction, it could be that Sasuke's unyielding thirst for power and his disregard for the consequences of his actions on those around him are reasons Naruto doesn't forgive him. Sasuke was so focused on his own goals that he often trampled on the feelings and safety of others, and Naruto, who is all about protecting and connecting with people, may find it hard to forgive such self - centered behavior.
Well, perhaps in this fanfiction, Kushina did something that violated Naruto's principles. Naruto has always been about loyalty and hard work. If Kushina did something like betraying the village or his friends, Naruto, being the stubborn and principled person he is, might not forgive her. Also, it could be that Kushina was absent during some crucial moments in Naruto's life and he holds a grudge for that.
One possible reason could be years of neglect. Maybe his family was absent during his difficult childhood in Konoha, leaving him to fend for himself. He had to endure loneliness and the scorn of the villagers without any family support, which could lead to deep - seated resentment and an inability to forgive.
It might be due to hidden secrets. If there are dark secrets within Konoha that Naruto discovers in the fanfiction, such as a conspiracy that involves some of the higher - ups. This would make him lose trust in the village as a whole.
One possible reason could be a traumatic event. Maybe he witnessed something so horrible that it made him shut himself off from everyone. For example, if he saw his friends in great danger and couldn't save them in time, it might have led to his silence as a form of self - blame.
Perhaps he's under a powerful genjutsu. In the Naruto universe, genjutsu can manipulate a person's perception and behavior. It's possible that an enemy has cast a genjutsu on Naruto that makes him believe that if he talks to anyone, something bad will happen to them, so he chooses to remain silent.
It could be that Sakura has done something that has disappointed Naruto deeply. This could range from her making a decision in a mission that Naruto didn't agree with, to her not being there for him during a difficult time. These actions might have gradually eroded his love for her.
One possible reason could be that Naruto has had some past experiences within the team that made him feel betrayed or let down. Maybe there was a mission where he thought his teammates didn't have his back. Another reason might be that there are secrets among the team members that Naruto has discovered, and these secrets make him question their loyalty. For example, if one of his teammates was hiding a connection to an enemy, Naruto would naturally start to lose trust.
Perhaps Naruto is focused on his own personal growth and training. He might see the yaoi relationships around him as a distraction from his goals of becoming a stronger ninja. He could be thinking that engaging with others involved in yaoi would lead him astray from his path of self - improvement.