Percy may try to keep himself busy by helping others. He would volunteer for more dangerous missions to distract himself from the pain of separation. However, in the back of his mind, he is always thinking about Annabeth and looking for any sign or clue that could lead to their reunion.
Percy might be really depressed at first. He would constantly think about Annabeth and the times they had together. He might isolate himself from his friends for a while, just sitting by the water and reminiscing.
He could also turn his pain into motivation. Percy would focus on training harder, becoming a better fighter and leader. He hopes that when they are reunited, he can protect Annabeth better. He might also start looking for ways to break whatever force is keeping them apart, going on mini - quests to gather information.
One idea could be that Percy gets sent on a quest in a different realm while Annabeth is stuck in Camp Half - Blood dealing with internal camp issues. This separation could lead to both of them growing individually. Percy might learn new powers or make new allies in the other realm, and Annabeth could strengthen her leadership at the camp.
Percy might stand up for himself. He could use his own skills and strengths, like his control over water if that's part of the fanfiction's universe, to show Annabeth that he's not an easy target.
One possible reason could be a misunderstanding. Maybe Percy does something that Annabeth misinterprets, leading to a rift between them. For example, Percy might make a decision during a battle that Annabeth thinks is too risky and endangering others, and this causes a big argument that results in their separation.
He could become withdrawn. Percy is a sensitive person at heart. So if Annabeth's actions are really hurtful, like if she cheats on him in a fanfic (although it's a very sad scenario), he would likely isolate himself from her and their friends. He might go off on his own to think things through and deal with his pain privately.
Annabeth would be in a tough situation. On one hand, she has to take care of herself and the baby. On the other hand, she's desperate to find Percy. She may be feeling a mix of fear, anger, and determination. She could be using her intelligence to analyze any clues that might lead to Percy's whereabouts. She might also be reaching out to any allies she has in the mythological world, asking for their help in finding Percy.
A simple plot could be that they are separated by a powerful spell. Percy is on one side of a magical barrier that he can't cross, and Annabeth is on the other. They can see each other but can't reach out. This would force them to communicate in other ways, like through telepathy if there's some kind of magic involved. It could also lead to them finding ways to break the spell from their respective sides.
She might initially be shocked. Annabeth is a strong character, so she could start by trying to stand up to Percy verbally, asking him why he's being so mean.
At first, it might become strained. Annabeth could be hurt and pull away from Percy. She might not want to be around him as much.
She might be initially very angry. Annabeth is intelligent and perceptive, so she would likely feel betrayed that Percy thought he could deceive her. For example, if Percy lies about a mission, she could find out the truth later and confront him immediately, demanding an explanation.
Annabeth might be initially in awe of Percy's new godly status. But she would quickly start thinking about how to use this new situation to their advantage. She is practical, so she would likely start planning how they can better protect their friends and the world.