He messed up.
He messed up big time all those years ago when they were adolescents.
"I don't want your help, filthy mudblood…!"
She made it clear they were not friends anymore. She cut off all ties and connections with him. They didn't sat and did homework together anymore, ate meals together, had tea…
He was angry at Lily. Why did she had to be so stubborn? If only she was willing to forgive him, to see past his mistake, there wouldn't be bad blood between them anymore.
He was angry at himself. Why did he call her that horrible name? Was it spending too much time with Lucius and the others in Slytherin that made him this way? He picked them over Lily…
She was the one who saw the real him. Who understood him. Who actually cared about him. She was the only one who saw him. She saw through him, better than anyone else…
And now she was gone.
The Dark Lord came and took her life. She was married and had a kid. A child that was of her and that arrogant slob.
If only he had said things differently… If only he had the strength and picked her instead of them, everything would be so different.
He tried to stop caring for her, but he couldn't. He realized he would always care for her. Even in death.
She had his heart from the start.
Always.
Song inspiration: Till I Hear You Sing - from Phantom of the Opera's sequel 'Love Never Dies'