He never said he changed his mind if he has please provide link. There has been lots of development between Naruto and Hinata, at first Hinata could barely speak when the series first started, but she was able to confess her feelings and was ready to die for him. Plus Naruto was paying alot more attention to Hinata when he reunited with his friends in the war arc. She knew it was him just by his eyes when his friends doubted if he was the real Naruto.
Plus, Hinata stated that when this war is over she intends to walk hand in hand with Naruto. She made it clear she intends to settle things with Naruto one way or another.
As for Sakura and Naruto development while they are closer friends Sakura still loves Sasuke. Plus it seems like the chances of romance between them lessened after the Five Kage summit arc with the false confession thing, Naruto was shown to be furious about it. Sakura did it because she doesn't want Naruto to love her, Sai said that Sakura wanted Naruto to hate her as her attonement.
Plus as I said before in the chapter the Path to Radience, Hinata made it clear that she is going to settle things with Naruto.
Oh and I reccomend you watch DBZ, the whole show can be found online. You will see lots and lots of Parrellels with Naruto. Kishi was inspired by DBZ. He based the main character off of Goku the hero of DBZ.
I know he inspired Naruto from there.
As for providing, dunno, it was an older interview with Kishi, hopefully I'll find it again.
He was paying more attention to her because she was the one being the most down out of everyone. Of course she needed more attention.
The rest comes only from Hinata's part, not Naruto's.
Even if she does something, Naruto hasn't been showed to stop loving Sakura.
And sorry, but since when Sai is an expert of human feelings?
Sai is used only as a tool to deceive, make it more "clear" when it's actually unclear.
Naruto wasn't furious, he just got serious. That's another thing.
And the 5 kage summit confession holds so many hidden stuff.
Why do you think it's the second time when Sakura's character is implied next to Naruto love situation?
She first says she likes him and then she lets her feelings free for a moment not being fully aware and once again, just like in the Orochimaru's follow, when it comes to be Sakura = love Naruto, Kishi interrupts things.
Doesn't it seems suspicious? If he wouldn't had nothing to hide, he would have let it go from the first time.
As for Goku and Chi Chi or whatever, until I don't know the settling myself, I won't say anything.