One way is by delving into his past traumas more deeply. For example, his loneliness as a child could be explored further to show how it led to his trust issues. Maybe in the fanfiction, Naruto has a series of flashbacks that make him question every new relationship he forms.
Betrayal is a common theme. Since Naruto has trust issues, fanfictions often explore how past betrayals, either real or perceived, have affected him. For instance, if someone he thought was a friend turned out to be working for an enemy.
One possible reason could be past betrayals. Maybe he has been let down by people he thought were friends in the fanfiction world. For example, if someone he trusted shared his secrets which led to him getting into trouble.
One reason could be betrayal by his friends. For example, if someone he considered a close ally made a deal with his enemies behind his back, it would shatter his trust. Another might be lies from the village leaders he respected. If they hid important information or manipulated him for their own gains, Naruto would start to question who he could trust.
One issue could be that it might distort the original Naruto story. Fanfiction is often creative but when it involves abuse, it can create a negative and untrue perception of the Naruto universe. It may also be disturbing to some fans who love the positive and heroic themes of the original work.
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.
One possible reason could be miscommunication. Maybe Kakashi has been involved in some secret missions or decisions that Naruto doesn't understand, leading to a breakdown in trust. For example, if Kakashi made a call during a battle that put Naruto or his friends in danger without fully explaining it to Naruto later.
His lack of trust could lead to a lot of misunderstandings. For instance, if someone tries to help him but he misinterprets it as a malicious act because of his distrust. This can create a cycle of more distrust as others start to feel frustrated with him.
It could be due to miscommunication. In the fanfiction, perhaps there were misunderstandings within the family. For example, Naruto might have overheard something that made him think his family didn't have his best interests at heart, but in reality, it was all a big mix - up. So, he gradually lost trust in them.
It could also be due to Sasuke's secrecy. If Sasuke is constantly hiding things from Naruto, like his real intentions or new powers he's acquired, Naruto would naturally start to feel that he can't trust him. Trust is built on honesty and openness, and if Sasuke is being cagey, Naruto's trust in him will fade.