One reason could be that he was framed for a crime he didn't commit and had to run away to clear his name. In the complex world of the fanfiction, there could be a conspiracy against him. Some powerful beings might not want him to be with Annabeth or have a child, so they set him up and made him disappear.
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.
Well, one possible reason could be that Percy made a really stupid decision without consulting Annabeth first. Like, if he went off on a dangerous mission on his own when they were supposed to be a team. Annabeth is a very strategic person and she might feel betrayed or extremely frustrated by such actions.
It could also be due to some sort of magic or mind - control. A powerful enemy might have cast a spell on Annabeth, forcing her to turn against Percy. In this case, it's not really her own will but the result of external manipulation.
One reason could be that she's scared. The idea of becoming a mother at that point in her life might be overwhelming, and she might think she can't handle it with Percy. Maybe she wants to protect Percy from the difficulties that come with the pregnancy as well.
One possible reason could be a misunderstanding. Maybe she saw Percy doing something that she misinterpreted as a betrayal of their friendship or their cause. For example, if Percy was seen talking secretly with an enemy, Annabeth might jump to conclusions without knowing the full story.
One possible reason could be jealousy. Maybe Percy gets more attention or recognition in their fictional world that makes Annabeth envious and thus appear to hate him.
In the fanfiction world, their personalities might be very complementary. Annabeth is intelligent and strategic, while Percy is brave and impulsive. This yin - yang dynamic could lead to a strong attraction, and the want to kiss could be a natural outgrowth of that attraction.
Perhaps Annabeth made a decision without consulting Percy that put him in danger. In the fanfiction world, this could lead to her feeling guilty and apologizing. For example, if she led their group into a trap because of her over - confidence, she'd realize her mistake and say sorry to Percy.
Maybe he was hit by some magic or a spell that affected his memory. It could also be due to some sort of trauma he experienced that made his mind block out his memories of Annabeth.
Maybe she's scared because the fanfiction portrays Percy in a way that's out of character for him. Like, it might show him being overly aggressive or having strange powers that she doesn't recognize, which makes her feel like she doesn't really know him anymore.