Percy might initially be in shock. He has always trusted Hestia, so when she betrays him, it would be a huge blow. He could become very angry and feel a sense of deep betrayal. He might lash out at those around him, or he could go into a state of self - doubt, wondering what he did wrong to make Hestia turn against him.
Percy could be heartbroken. He might isolate himself for a while, feeling that he can't trust anyone anymore. However, as time passes, he would realize that he can't just give up. He would use his pain as fuel. He would start to investigate Hestia's actions more closely, looking for any clues that could help him turn the situation around. Maybe he would discover that Hestia was forced into this betrayal, and then he would have to decide whether to forgive her or not.
He could be angry. Percy might lash out at those who betrayed him, feeling a deep sense of injustice. He would probably be determined to prove his innocence and get revenge on those who wronged him.
At first, Percy would likely be angry. He's a fighter, and being betrayed by someone he loves would fuel his rage. He might go after Annabeth to demand an explanation. But as the reality sinks in, he could become very sad and withdrawn. He might isolate himself from his other friends as well, feeling like he can't trust anyone anymore. He would constantly be thinking about what he did wrong to make Annabeth turn on him.
At first, Percy could be in shock. He can't believe that the gods, whom he has served and trusted, would betray him. But then, as the reality sinks in, he might become determined to get justice. He starts to plan his next moves carefully, using his wits and the skills he has learned over the years. He may also feel a sense of sadness and loneliness, as he realizes he is now on his own against the powerful gods.
Percy could initially feel shock and disbelief. He might try to talk to Poseidon to find out why he was betrayed. If that doesn't work, he could become angry and lash out, perhaps even challenging Poseidon directly.
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.
Percy might feel a deep sense of hurt. He values friendship highly, and this betrayal would make him question who he can trust. He could become more guarded and less likely to trust new people easily. Reyna would be more focused on the bigger picture. She would see the betrayal as a threat not just to herself but to the stability of the demigod world. So she would start gathering her allies, those who still believe in her, and form a strategy to counter the false accusations and the forces behind the betrayal. She would be determined to prove that she and Percy are not the traitors they are made out to be.
Perhaps Percy would try to understand the primordial's reasons for the betrayal. He's a smart and empathetic character. He might think that there was some misunderstanding or that the primordial was forced into it. So, instead of immediately retaliating, he could try to communicate with the primordial to clear things up. If that doesn't work, then he would be more likely to take a defensive stance rather than an offensive one, at least until he fully understands the situation.
Percy would most likely be extremely confused and frustrated. He has been through a lot already in his life as a demigod. Being forced into a marriage with Hestia would seem like another huge and unwanted burden. He may initially feel powerless against the will of the gods, but then his determination would surface. He'd start looking for ways to either change the situation or at least make the best of it while still maintaining his own identity and relationships with his friends.
Percy might initially be confused. He might start to question everything that led up to the betrayal. His mind could be racing, trying to figure out if there were any signs he missed. He might also be hurt, but the confusion could overshadow the pain at first as he tries to make sense of the situation.
Well, it could be that Hestia betrays Percy for power. In the fanfiction world, she might see Percy as a threat to her own influence among the demigods or the gods. So she makes a deal with another powerful entity to get rid of Percy. For example, she could give false information about Percy's next move to a group of monsters, causing them to ambush him.