Jason and Piper would probably be supportive as well. Piper might tease them a little in a friendly way, like 'You two are so cute it's almost sickening'. Jason would likely be more reserved but still show his approval with a nod and a smile.
The younger campers would look up to them even more. They would see Percy and Annabeth's love as something to aspire to. Some of the younger girls might giggle and the boys might be a bit jealous but overall, everyone at camp would be glad to see their relationship strengthen with those words.
Their friends like Grover would be really happy for them. Grover has been with Percy through a lot and he knows how important Annabeth is to Percy. He might give them a big, goofy grin and say something like 'It's about time!'.
They might be a bit in awe at first. She has a certain presence about her that comes from her being a demigod. Maybe they're curious about her and ask Percy a lot of questions about her later.
Well, some of their friends might be really excited for them. Hazel would see it as a positive development, thinking that they are a great couple. Frank might be a bit shy about the whole thing, but still give them his祝福 (blessing). However, there could also be some friends who are a bit concerned. Thalia, for example, might worry that their relationship could get in the way of their demigod duties. She would be afraid that they would be too focused on each other and not on the important tasks at hand. But overall, most of their friends would probably adjust to the new relationship fairly quickly.
Then, she would probably be angry. Annabeth is a strong - willed character. She would feel betrayed and used, and her anger would fuel her to find out the truth. She might start her own investigation to figure out what's really going on with Percy, whether he's been influenced by someone or if there's another reason for his actions.
Grover would be super excited. He'd probably start bleating happily and immediately start thinking about all the great food he could eat at the wedding. Jason would be very supportive and offer his help in any way he could, like with security for the big day. Piper would be thrilled and would probably start planning Annabeth's bachelorette party right away. Leo might crack some jokes about Percy finally tying the knot but deep down he'd be really happy for them.
Grover would probably be really excited. He might bring all kinds of nature - related gifts for the baby, like a special plant that has protective powers. He would also be very protective of the baby, using his nature senses to detect any danger.
Some might be excited. They've probably heard a lot about Percy from Annabeth, so they are eager to meet him in person.
Some of Percy's classmates might be in awe of Annabeth. She's smart and confident, so they could be a bit intimidated at first. But then they start to admire her for her knowledge.
Their friends at Camp Half - Blood would be overjoyed. Grover would probably be dancing around and playing his reed pipes in celebration. The other demigods would see it as a sign of hope, that love can thrive even in their dangerous world. They would start planning a huge party with lots of food and games.
Jason and Piper would be very supportive. They'd offer their help, like babysitting or providing resources. Piper might use her charm - speak ability to soothe the baby when it's fussy, and Jason could use his leadership skills to help Percy and Annabeth make important decisions about the baby's future.
Some of Annabeth's friends could react with laughter and jokes, while others might be a bit flustered and not know how to act. It really depends on the personalities of the friends in the fanfiction.