One possible reason could be jealousy. Naruto is very powerful and some in Konoha might be envious. For example, some minor clans might feel that Naruto, as an outsider in a sense, gets too much attention and resources. Another reason could be fear. His Nine - Tails power is so immense that some might fear he could lose control and endanger the village, so they betray him to try and eliminate the 'threat' before it's too late.
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.
Naruto would likely be extremely hurt. He has always considered the Konoha 11 as his friends and comrades. So, at first, he would probably be in denial, trying to figure out what went wrong. He might try to talk to them, to understand their reasons.
One possible reason could be a misunderstanding. Maybe some false information was spread in the village that made Konoha believe Naruto had done something wrong. In fanfiction, things can be exaggerated and misinformation can easily lead to a situation of betrayal.
One possible plot could be that Naruto's incredible power makes the Konoha elders or some jealous shinobi feel threatened. They might spread false rumors about him being a danger, leading to the village turning against him. Maybe they frame him for a crime he didn't commit, like a powerful attack on the village that was actually the work of an enemy they secretly allied with. This would make Naruto, who has always been loyal to Konoha, feel extremely betrayed.
In these fanfictions, it might be related to the secrets Naruto holds. For example, if he discovers something about Konoha's dark past that certain people don't want exposed. They would then try to get rid of him by making him look like a traitor. Also, there could be external forces influencing Konoha to turn against Naruto, like other villages spreading false rumors.
Well, in this fanfiction scenario, Naruto might be betrayed by Konoha due to the long - standing distrust of the Nine - Tails within him. When he joins Kumo, he could be used as a weapon against Konoha at first. However, Naruto being Naruto, he would try to change the Kumo way from within. He'd show them that power isn't everything and that friendship and loyalty are important too. This could lead to a change in Kumo's attitude towards Konoha and even start a new era of cooperation between the two villages.
He could be initially shocked and heartbroken. Naruto has always been loyal to Konoha, so such a betrayal would hit him hard. He might go into a state of disbelief for a while.
Naruto would probably be very angry at first. He has always considered Konoha his home and to be betrayed by it would be a huge blow. He might initially try to reason with the villagers, thinking it's a misunderstanding. Hinata, on the other hand, would be more likely to be heartbroken. She's more reserved and the thought of her village turning against her would be deeply painful.
He would be devastated. Naruto has always considered Konoha his home and the people there his family. At first, he might not believe it, thinking it's all a misunderstanding. But as the truth sinks in, he would probably be filled with anger and sadness. He might leave Konoha, but his sense of justice wouldn't let him just forget about the betrayal. He could seek revenge on those who wronged him, or he might try to prove his innocence from afar.