It could also be due to outside influence. An enemy might deceive Naruto's team into believing that Naruto has turned against them. The enemy could plant false evidence or use mind - control techniques on the team members, causing them to turn on Naruto without realizing the truth.
One possible reason could be jealousy. Maybe Sasuke in the fanfiction becomes jealous of Naruto's growing power and decides to betray him for his own gain. Another reason might be a misunderstanding. For example, if Naruto is wrongly accused of something terrible, and the rest of Team 7 believes it without giving him a chance to explain, they could turn on him. It could also be due to outside influence. Perhaps an enemy manipulates Team 7 into believing that Naruto is a threat to them, leading to their betrayal.
One possible reason could be that she was forced to betray him. Maybe an enemy got to her family and threatened her to turn on Naruto. For example, in the Naruto universe, there are many powerful villains who would stoop to such tactics.
It could be due to a power imbalance. If Naruto's power as Hokage makes her feel overshadowed or unimportant, she might be led to betray him. Also, perhaps she discovers some long - hidden secret about Naruto that she can't forgive, like a connection to a past enemy or some dark side of his shinobi past that he has kept from her.
One reason could be that his team discovers some kind of hidden power in Naruto that they fear. Maybe they think he's too dangerous to be around, so they abandon him. Another possibility is that they are influenced by some outside force, like an enemy who convinces them that Naruto is a liability.
One possible plot could be that Team 7 is manipulated by a powerful enemy. Maybe Orochimaru manages to cast a powerful genjutsu on them, making them believe Naruto has turned evil. So they turn against him. It could also be that they are forced to choose between Naruto and the safety of the village in some extreme situation and they wrongly choose to sacrifice Naruto.
One possible reason could be fear. Naruto is extremely powerful, and some in Konoha might fear that he could one day lose control of his power. Another reason could be political intrigue. There may be certain factions within Konoha that see Naruto as a threat to their power and influence. Also, jealousy might play a part. Naruto has achieved so much and has the love of many, and some might be jealous and thus plot against him.
One possible reason could be that she is influenced by an enemy. Maybe the enemy has some sort of leverage over her or has brainwashed her into believing that Naruto is a threat. Another reason might be a misunderstanding. For example, she could misinterpret Naruto's actions as being unfaithful or harmful when in reality he has good intentions. It could also be due to her own insecurities. If she feels overshadowed by Naruto's popularity and power, she might betray him to assert her own identity.
One possible reason could be a misunderstanding. Maybe there was some false information spread about Naruto that made Team 7 believe he had done something unforgivable. For example, if an enemy framed Naruto for attacking the village secretly, and Team 7 fell for it without proper investigation.
In this fanfiction, it might be that a misunderstanding is at the core. The village elders could spread false rumors about Naruto having some sort of dark power. Team 7, believing these rumors, decides to side against Naruto. Haku, who has his own motives related to the power struggle in the ninja world, takes advantage of the situation. He could manipulate Team 7 into thinking Naruto is a danger and needs to be stopped, which would be a heartbreaking betrayal for Naruto.
Perhaps Naruto quits Team 7 in the fanfiction because of a betrayal. He might find out that one of his teammates has been secretly working against him or has lied to him about something really important. This could shatter his trust in the team and make him want to leave. Or it could be due to an accumulation of small incidents. Like constantly being the one to get in trouble for the team's mistakes, or not having his opinions heard when it comes to team strategies. Over time, these little things can build up and make him feel that he's better off on his own.