She could be angry. Anger is a common reaction to betrayal.
Well, Sakura could also try to understand why her friends betrayed her. She might be the kind of character who looks for the root cause of the problem. She could approach her friends, not to forgive them right away, but to have a conversation. By doing this, she hopes to find out if there was some misunderstanding or if they were forced into betraying her.
Sakura could become very angry. She has been let down by those she trusted, and anger is a natural response. She might lash out at her friends or distance herself from them immediately. For example, she could say some harsh words to them in the heat of the moment.
He might become very withdrawn. Bell could start to isolate himself from others, especially those associated with Hestia. He may no longer trust as easily as he did before.
He probably feels extremely hurt and confused. Betrayal by friends is a very painful experience, and Bell might question his own judgment in trusting them in the first place.
At first, Harry would be in disbelief. He would think it was some sort of joke or misunderstanding. But as the reality sets in, he would become a bit of a loner. He'd still have his sense of right and wrong, so he might continue to fight against the dark forces on his own, all the while hoping that his friends would come to their senses and realize they made a huge mistake in betraying him.
He would be heartbroken. Naruto values friendship above almost everything. At first, he might not believe it and try to reason with his friends.
Bell could be deeply hurt by the betrayal. She might start to have nightmares about it. As the story progresses, she could find the strength within herself to confront her so - called friends. She could demand an explanation and then decide whether to forgive them or cut them out of her life completely. She might also become more cautious in making new friends in the future, always being on guard against potential betrayal.
She might become extremely angry and cut off all ties with Draco immediately. Hermione is a strong - willed character, so she would not tolerate betrayal easily. She could use her magic to create some sort of barrier between them, magically locking him out of her life.
Ash could respond in different ways. He might try to confront his friends immediately to get an explanation. If the betrayal is really bad, he could cut them off completely and focus on his own goals, like becoming a better Pokémon trainer. He would also probably have some internal struggles, as he has memories and experiences with these friends that he can't just forget.
He might be extremely hurt. Harry could go into a state of shock and disbelief at first. He may isolate himself, not wanting to trust anyone else for a while.