that was because she made him feel that way.
Namine changes Memories, not emotions. The interaction Sora "remembered" he had with Namine made him believe she was more than a friend, which was a stronger emotion for what he felt towards Kairi from the true interaction he had with her.
Seems like the emotions didn't really pass over going by KH2.
well, whatever. Sora/Kairi is more canon than anything else.
Nothing is canon in KH as Nomura stated he wanted to leave it up to the fans.
And I fail to see how Sora is more canon with the girl he pushed away, than with the girl he believed was more than a friend.