Light

Preston had never met another human being that personified their name as much as Luz Morales. Light. She had come in and lit up his life unasked and he got so used to it that he couldn't bear to go back to the darkness. 

From very early on in their friendship, there was a noticeable hole inside him when she wasn't around. That was why he was so relieved when she started including him in all of her family's vacations and holidays. He still had to go "home" for part of it but anything was better than nothing. 

It didn't take long for him to reach a point where school felt more like home than his father's house ever did. And it had nothing to do with the school itself. Home was wherever Luz was. 

She was so bright and sunny that even someone as generally apathetic as him had come to feel things. All because of her.