Hermione.
Harry was devastated. Draco was standing right next to him.
"Why are you here?" Harry asked, somewhat aggressively.
Draco was surprised by that question. "I was worried about you." He said, and then added. "I care about you."
"And her?" Harry pointed towards Hermione. "Do you care about her?"
"I…" Draco started saying hesitantly.
"Do you?" Harry now yelled. Draco had never seen him this angry.
"I do." Draco said quickly. Does he though?
"No, you don't! You only care about yourself." Harsh.
"That's not…"
"You didn't care when the chamber was opened, you didn't care when any of the other victims were attacked, why do you care now?" Harry cut him off, before he could object.
"I care because you do." Draco yelled back. Not angrily, just loud enough so Harry could hear him over his own yelling. "I care about you." He said then, calmly.
Harry, very emotional at this point, collapsed to his knees, covered his face, and wept. Draco simply moved towards him, knelt beside him, and wrapped a hand around him.
"I'm sorry," Harry cried.
"No, no. It's okay." Draco tried to comfort him. He looked towards Hermione's bed, and he felt… guilt?
Harry looked up. Stopped crying.
"Did you hear that?" He asked, "of course you didn't." He answered his own question, and then he took off.
"Wait!" Draco tried to stop him, but Harry was gone.
Harry followed the voice throughout the castle, all the way to Moaning Myrtle's bathroom, where he found the diary. That's where it all made sense.
"Myrtle!" Harry called.
Moaning Myrtle flew out of one of the stalls.
"How did you die?"