Perhaps Percy's loved ones are made to believe false rumors about him spread by an unknown enemy. As a result, they turn their backs on him. Percy would need to find a way to expose the real culprit behind the rumors and regain the trust of his friends and family.
He would likely be angry. Percy has a temper, and being betrayed by someone he thought was an ally would fuel his rage. He might lash out verbally or even physically, depending on the situation. For example, if they were in a battle together and Artemis suddenly turned on him, he would have to defend himself while also dealing with the emotional turmoil of the betrayal.
Percy might initially feel a great deal of anger. He's been wronged by those he thought were his friends. But then, with Annabeth by his side, he could start to focus on finding out the truth. He might use his skills, like his combat abilities and strategic thinking, to figure out who or what is behind the betrayal.
It could be an old enemy from their past, like a resurrected Titan or Giant. These powerful foes might manipulate Percy and Jason into betraying their friends as part of a grand plan to regain power or take revenge on the demigods.
In the fanfic, there could be a big revelation later on that it was all a misunderstanding. Maybe some sort of mind - control magic was involved. But until then, Percy would have to face many challenges alone. He might even start to question his own worth and abilities. For example, he could be hesitant to use his powers, thinking that if his friends could betray him, maybe his powers are part of what made them turn away. It would be a very emotional and angsty journey for Percy as he tries to figure out what went wrong and how to fix it.
In this fanfic, it could be that Percy and Jason are under the influence of a magical spell or a powerful charm. This influence makes them act against their normal moral compasses and betray their friends. The story could then focus on how their friends try to break the spell and bring them back to their side, while also dealing with the consequences of their betrayal.
One possible reason could be jealousy. Maybe Percy has some special abilities or achievements that make others envious. For example, his connection to the sea could be seen as a huge advantage that others might resent. Another reason could be misinformation. Someone might spread false rumors about Percy, leading others to believe he's done something wrong when he hasn't. It could also be that there's a misunderstanding about his relationship with Annabeth. Some might think he's getting special treatment from her or the other way around, which causes them to turn against him.
Well, one possibility is that the gods who betray Percy might be jealous of his power or popularity among mortals. Maybe they feel threatened by his ability to influence the mortal world in a way they can't control. They could start spreading false rumors about him, turning some of his allies against him.
One aspect could be that in many Percy Jackson - related fanfictions, Percy being betrayed by the gods often leads to a complete shift in his character arc. He might become more cynical or distrustful. For example, he could start to question his previous heroic deeds and wonder if he was just a pawn in the gods' games all along.
Apollo might be the betrayed god. He could have been tricked by another god into betraying Percy. For example, Apollo might have been promised more power or a higher status among the gods if he turned against Percy. But then he realizes too late that he's been used and that he's actually betrayed someone who could have been an ally.