A little background: Annabeth used to adventure with Hermes's son Luke. Over time, Annabeth developed a crush on Luke. As Annabeth got older, Luke developed feelings for her, too. Luke turned evil. Hermes blamed Annabeth for not preventing Luke from turning evil. Annabeth blamed Hermes for being a rotten dad and giving Luke the capacity to become evil in the first place. Luke died in war. Hermes and Annabeth blamed each other. Confused? Welcome to my world.
"The Demigod Diaries". Book by Rick Riordan, August 14, 2012.