It was simply wrong. Anybody could tell that. A Percy without his Annabeth. She was his other half, his soul mate. And they had been through such worse things and had yet ended up together. But never had Percy thought that death could do them apart. He had begged to Nico, if he could bring her back. But somewhere inside, he knew she was gone. But he just refused to believe.
Even Sally couldn't calm him down. He kept busting into the Athena cabin, expecting to see Annabeth pouring over books, look up at him and call out, "Hey Seaweed Brain!"
When he finally came to terms with the fact that she was gone, he poisoned himself that night. Percy was never again that excited to his Wise Girl.