It was a slow and steady process.
Up until Naruto VS Kaguya I was a diehard Naruto fan. But then as soon as he called Obito the coolest guy, it all went downhill from there. He started becoming less mature with the things he was saying until I realized... 'this guy has no resolution to peace except shooting down everybody elses.'
I then decided I was officially done with the character that was Naruto when he decided he couldn't kill Sasuke. He had a weak mentality, and regardless of how 'good' or 'positive' it was, it was unrelatable and over extreme. He was about to kill the Kage, seal all the tailed beasts and make himself an enemy to the world and Naruto still didn't have the nads to just end him. I understand the 'because you're my friend' stuff but that line gets old QUICK. That's been his excuse the entire manga, but it never bothered me up until the last fight. Right then and there Sasuke became a lot more appealing simply because he's what Naruto isn't; relatable and realistic. Bottom line is, his resolution would've worked out. Bottom line is, Naruto's only came to fruition because of MC stability.