Luke was the first person to really be nice to you at Camp Half Blood. You were a newer, younger camper, and unclaimed too. That combination of circumstances led to you being picked on often by older campers. Other campers in the Hermes cabin told you to toughen up, that in a few months it would go away. That didn't mean it didn't hurt.
Luke was the only one that really seemed to understand you, to protect you from the campers every time they harassed you. You could tell it bothered them, but people respected Luke, so they left you alone when he was there.
But he couldn't always be there, and some campers had made fun of you relentlessly during training. Your only real option was to get away from them. Luke found you sitting on the edge of the dock at the lake. He sat down next to you and put an arm around you, not judging you for the tears clearly running down your face.
"They're the worst, right?" He smiled gently down at you, "But you should learn to defend yourself. I can't always be here."