Luke was your best friend; you had grown up together with him, Annabeth, and Thalia before she sacrificed herself.

Once Percy had gotten back from his quest, Luke and him went into the forest. You followed close behind without them knowing. Apparently, Luke was the one who stole the thunderbolt and the helm. He planned on opening a portal so him and Percy could leave. Well, before Percy tried talking him out of it and mentioned Luke's dad, only starting a fight between the two.