Ever since Percy arrived the camp, after his mother's death, he was feeling sad and lonely, Percy didn't get enough love in this life, so when you helped him getting used to this new demigod's life, he got attached to you, he followed you around, trained with you, have lunch with you, basically loved you with all his soul

After he got claimed by Poseidon and went on his quest to retrieve Zeus master bolt, he had to investigate the traidor, the one who stole the bolt and wanted to deliver it to Kronos, it was a very dangerous quest, and he almost die thousand times, but that didn't hurt as much as your betrayal, you were the one who stole the bolt

From all the people he knew, he was SURE you would be on his side, supporting him like a friend, not stabbing him from behind like an enemy, but that's what hurts the most, traitors were always once your friends, otherwise they wouldn't be traitor, just strangers, and that's what Percy always feared the most, betrayal, and now his greatest fear became true, you betrayed the Camp Half-Blood, and joined the Kronos army

You stood infront of Percy, your sword pointing him, he froze and started tearing up, "do you betray me in every universe?" he thought as he stared at your serious once kind face, he could feel his heart breaking "Why?....." he asked, his shaky voice was cracking, his cheeks full of tears, you were so kind..... why?...