Some of his other friends might react differently too. Some may be more cautious around him, worried about the power of the jinchuuriki within him. But those who truly trust Naruto, like Shikamaru, might not change their attitude much. They would see that Naruto is still the same person he was before, just with this added aspect to his identity.
She might be initially shocked. Sakura has always seen Naruto as a friend, so learning of his romantic feelings could completely change her perspective of him. It could make her re - evaluate all their past interactions.
Well, in this kind of fanfic situation, Sakura could also become more protective of Naruto. Since a jinchuuriki is in a rather dangerous position, she might start to see him as someone who needs her support more than ever. She could try to keep his secret safe from those who might want to harm him because of it.
In many fanfictions, it might start with Sakura noticing small things about Naruto that she hadn't paid much attention to before. For example, his unwavering determination in the face of difficulties. This newfound awareness gradually grows into admiration and then love as she spends more time with him, either on missions or during downtime in the village.
Another development could be that Sakura starts to develop feelings for Naruto as she spends more time thinking about his love for her. She might notice things about him that she never paid attention to before, like his kindness and determination in a more romantic way.
He might be initially shocked. Naruto has been so focused on his goals like becoming Hokage that he may not have expected Hinata's love. He could be really touched that someone as kind and gentle as Hinata has had such deep feelings for him all this time.
One reason could be that Sakura is confused about her own feelings. Maybe she has feelings for someone else and doesn't know how to handle Naruto's obvious affection towards her, so she lashes out and ends up hurting him.
Naruto might initially be shocked and heartbroken. He may try to hide his pain and put on a brave face, as he has always done in the face of adversity. He could also become withdrawn for a while, distancing himself from Sakura as a form of self - protection.
Perhaps in the fanfiction, Naruto has had some bad experiences with Sakura. Maybe she has let him down in crucial situations, like not believing in him when he needed it most. This could lead to his feelings of despise as he feels betrayed by her lack of faith.
In a Sakura Cardcaptors fanfic where Chelsea finds out, she might react in different ways. She could be shocked and initially not believe what she has discovered. For example, if she finds out about Sakura's secret cardcaptor identity, she may question how such a thing could be possible in the seemingly ordinary world they live in.