This question has been discussed by many people, and Naruto's emotional line for the young field has undergone several changes. The first part only takes her as a friend, and there is no obvious change in the early stage of the high wind. The first change is that Payne attacked Konoha, and Naruto was stuck in the ground. When Naruto gave his life to save him, although Naruto couldn't say "change his mind" at this time, at least the status of Naruto in his heart was far from the same. The second time was ten tail, who endured the great war in the world. When Ningci died, they joined hands and merged with chakra. At this time, I believe that at least Naruto's emotional line has been deflected, but he is too nervous to understand the real intention of Ueda. It was not until the last that Kishimoto filled in all the previous pits for the plot, and then the two formally established a relationship. It is said that Naruto's emotional change is due to the fact that with the development of the plot, the popularity of Ueda has far surpassed that of KINOMOTO SAKURA.
For KINOMOTO SAKURA, Naruto's affection for him in the early stage can be said to be a kind of child's affection and jealousy for Sasuke. With Naruto's growth, he felt that KINOMOTO SAKURA's heart could not have other people's position except Sasuke, and it became a kind of fulfillment. He and KINOMOTO SAKURA have known each other since childhood and grew up together. All the joys, sorrows and even idiocy are naturally shown. When he established a relationship with Ueda, he had grown by leaps and bounds, and when he was more mature, he was naturally stable.