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.
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 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.
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.
Percy would be angry. He has been through a lot in his own world and being betrayed again would not sit well. He'd probably lash out with his powers at first.
He might be extremely angry and feel a deep sense of hurt. After all he has done for Poseidon and the gods, being betrayed would shatter his trust. He could go into a period of self - exile, distancing himself from the demigod world and trying to find his own path without the help of his father.
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 But as the reality sinks in, he could become very sad and withdrawn.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.
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.
Percy could initially be heartbroken. He's a very loyal person, and to be betrayed by those he considered family would be devastating. In Tartarus, he would have to rely on his instincts and his powers. He might also experience a lot of self - doubt, wondering if he really was as bad as they made him out to be. As time passes, he would start to plan his revenge against those who wronged him while also looking for an escape route.
Percy might be angry at first. He's used to being a loyal friend, so betrayal would hit him hard. He'd probably try to find out the truth and clear his name. Jason, being a more diplomatic type, might initially be shocked and then try to reason with those who betrayed him. Nico, on the other hand, could retreat into himself. He has a more solitary nature, and the betrayal might make him even more withdrawn.
The gods are always a possibility. Zeus, for example, has been distrustful of Percy in the past. If Zeus feels that Percy is getting too powerful or is a threat to his rule, he could engineer a situation where Percy is betrayed. He might use other demigods or even mortals to turn against Percy.