At first, Percy could be in denial. He might think that there's some misunderstanding, that Annabeth doesn't really mean to break his heart. So he tries to talk to her, to make things right. But as the truth sinks in, he could be really depressed. He might lose his appetite, not be able to sleep well, and just generally seem like a shell of his former self. His whole world revolved around Annabeth, and now that it's falling apart, he doesn't know how to cope.
Well, it could be that Annabeth betrays Percy's trust. Maybe she lies to him about something really important, like her true feelings or her actions. This lie could be the start of breaking his heart.
One possible plot could be that Percy makes a big mistake like getting involved with another girl out of misunderstanding or being forced into a situation that makes it seem like he's cheating on Annabeth. This would shatter Annabeth's trust and break her heart.
The story could end well if both Percy and Annabeth take some time apart to grow individually. Percy could learn from his mistakes and Annabeth could work on her trust issues. Then, they could meet again, see how much they've changed for the better, and fall in love all over again, stronger than before.
He could also become angry. Percy has a bit of a temper, and he might lash out at Annabeth, demanding an explanation. He might feel betrayed, especially if he doesn't understand the real reasons behind the break - up. In his anger, he could distance himself from their mutual friends and go on solo quests to clear his head.
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 He could become withdrawn and moody, shutting out his friends and allies.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.
Perhaps Percy realizes that their relationship has become too codependent. He might feel like he's losing his own identity within the relationship. He could also break up with Annabeth if he discovers some long - hidden secrets about her past that he can't come to terms with, like if there were things she did in the past for survival during a quest that go against his moral code.
One possible reason could be differences in their long - term goals. Maybe Annabeth is more focused on her architectural dreams and wants to study in a far - off place, while Percy is more tied to the demigod world in Camp Half - Blood. Another reason might be jealousy. If Percy spends too much time with other demigods, especially female ones, Annabeth could feel left out and insecure, leading to the break - up.
Well, it could be that Artemis, in the fanfiction, has to make a choice that goes against Percy's feelings. Maybe she has some divine duty that forces her to break his heart. For example, she might have to sacrifice their relationship to protect her hunters or to maintain some sort of balance in the mythological world.
The campers at Camp Half - Blood would be shocked. Some might take sides, especially those who are closer to either Percy or Annabeth. The Aphrodite cabin might be all up in the drama, trying to play matchmaker again to fix things. The Ares cabin might see it as a sign of weakness in Percy and try to pick on him a bit more. Overall, it would create a lot of gossip and tension around the camp.