Another possibility is that Artemis is actually relieved. She is a virgin goddess, and the relationship with Percy might have been a deviation from her normal way of life. So, she might see the break - up as a return to normalcy and be able to focus more on her own identity and the things she truly values like the hunt and protecting her maidens.
She could also be angry. Given her power and status, she might feel slighted by Percy. She may take some form of revenge, not in a malicious way but perhaps by making Percy's life a bit more difficult during his quests. For example, she could send her hunters to interfere or withhold some information that could be useful to him.
Percy might be devastated. He could become withdrawn and moody, shutting out his friends and allies. He might also be filled with anger and a sense of betrayal, which could lead him to make rash decisions.
He may also try to figure out what went wrong. Percy is a smart demigod, and he would likely not just accept the betrayal without trying to understand the cause. So, he might start investigating, talking to other characters who might have some insight, like the other demigods or even some minor gods who are friendly to him.
Perhaps it's due to the interference of the gods. The other deities might not approve of their relationship for various reasons. Maybe Zeus, fearing the power that could come from a union between Percy and Artemis, decides to put an end to it. In the world of Percy Jackson, the gods often meddle in the affairs of mortals and demigods, so this could be a factor.
Another way the story could develop is that there could be a chance for reconciliation later on. Maybe a new threat emerges that forces Artemis and Percy to work together again. Through this process, they start to understand each other better and realize that the reasons for the break - up were perhaps not as solid as they initially thought. However, this reconciliation would be a long and arduous process, filled with mistrust and hesitation at first.
She would probably be furious. Artemis has a strong sense of justice and protecting the vulnerable. So, she would likely immediately start to plan how to deal with those responsible for Percy's abuse.
One possible reason could be differences in their duties. Artemis is a goddess dedicated to chastity and the hunt, while Percy has his own quests and loyalties in the demigod world. Their paths might have diverged so much that it led to the break - up. Maybe Artemis felt that Percy's presence was starting to interfere with her commitment to her hunters or her own divine responsibilities.
In some fanfictions, Artemis might react with intense anger. She is a protector, especially of the innocent. So she could immediately seek justice for Percy, using her power and influence among the gods to find the perpetrator.
Initially, Percy is likely to be heartbroken. He thought he had a certain relationship with Artemis, whether it was friendship or respect. So when she betrays him for Orion, he may go into a state of self - doubt. He could wonder what he did wrong and start to isolate himself. But as time passes, he may gather his strength and decide to face Artemis and Orion head - on, to either regain Artemis's trust or show her the error of her ways.
He might be confused at first. Percy has always been a bit of an outsider among the gods, but he may not expect Artemis to hate him. So he would try to figure out what he had done wrong.
Artemis would be in shock initially. Given her status as a powerful and independent goddess, the idea of being forced into marriage is unthinkable. She would likely try to use her divine powers to break free from the situation. If she can't do it immediately, she might start to negotiate. She could offer other things in exchange for her freedom from this marriage. And if Percy shows any sign of taking advantage of the situation, she would not hesitate to put him in his place.