Answer and Explanation:
1. Because he felt the need to feel that someone, besides him, was alive there in the underworld where they were. When Annabeth held his hand, he was happy that she was alive and knew that she was happy for the same reason. They were giving each other courage and comfort.
2. Annabeth felt sad because Cerberus felt alone and without equal attention to how she felt about her family.
This question is about the saga "The Lighthing thief" that tells the story of Percy Jackson a boy who discovers that he is the son of Posseidon and lives several adventures based on Greek mythology.