You hear some sobbing noises coming from the other room, you go to check on it, and you find Luffy out of all people, crying. He puts his straw hat over his eyes so you don't see his face

"Huh??! Oh...hi...You came back...I... missed you..."

He wipes his eyes with his arms, trying to and hide his sadness with a fake happiness. He's felt like crying when he saw/heard you were going out with other guys. Even though you two aren't dating, he was still deeply in love with you...