Some fanfictions might show Percy getting angry. He could feel betrayed, especially if he doesn't understand the reasons behind the breakup. He might lash out, either verbally or by going off on his own on some dangerous adventure to deal with his emotions.
He might be initially in shock. Percy has been through a lot with Annabeth, so being dumped would come as a huge blow. He could be speechless for a while, unable to process what has just happened.
Well, Percy is a complex character. His reaction could depend on how much he knew about the pregnancy before Annabeth left. If it was a complete surprise, he might be in denial for a while. He could also start to blame himself, thinking he had somehow failed her. And then he might eventually turn that pain into a determination to be a better person, whether or not he ever sees Annabeth again.
Annabeth would be very shaken up. After the initial shock, she would assess the situation calmly. If Percy is unconscious, she would try to find a way to wake him up. She might talk to him, recalling their memories together, hoping it would reach him on some level. And she would be very protective of him while he's injured, not allowing any further harm to come to him. She would also feel guilty, thinking that if she were stronger or more careful, Percy wouldn't have had to protect her and get hurt in the first place.
He may become angry. Percy has a bit of a temper, so he could lash out at the situation or even at Annabeth if she's still around. He might feel betrayed and start to question all the things they've been through together. He could also go into a state of depression. Losing Annabeth, who has been such an important part of his life, could make him withdraw from his friends and activities. He may lose his motivation for quests and just mope around, feeling sorry for himself.
She might be grateful. After all, if she has a fear or aversion to spiders, Percy getting rid of it is a kind gesture.
Annabeth could also be angry, not at Percy but at the situation or the forces that led to his death. She might vow revenge and start on a journey to find out who or what was responsible for Percy's sacrifice and make them pay. This could lead her into a whole new set of adventures and challenges as she tries to come to terms with her loss.
She might be heartbroken at first. She could try to jog Percy's memory by showing him things that were important to them.
Well, he might be really flustered. Percy is often portrayed as a bit of a goof in some fanfictions. He could stutter and turn red, not really knowing how to handle the situation.
It could be that Percy's arrival disrupts the balance or routine at camp, which Annabeth doesn't like. Or perhaps there's some jealousy or competition involved.
She often reacts with annoyance. Since she's usually focused on important things like quests or helping her friends, unwanted advances can be a distraction. So she might give a cold stare or a curt response to shut the person down quickly.
Well, it depends on who is flirting with her in the fanfiction. If it's someone she doesn't like, she'll probably be dismissive and give cold responses. However, if it's someone she has a bit of an interest in, she could be coy and a bit shy while still maintaining her confident facade.