Severus and Lily Potter.

Severus was miserable. Not just now, but always. He knew that the kids all thought he was just evil, mean, horrible. He wasn't. He could smile. He could laugh. He could...love. Tears welled up in his eyes and he sank down into the chair at the front of the empty classroom and put his head in his hands. He musn't think about her. He opened a book and started reading, but her name filled the pages. He slammed the book. He hadn't allowed himself to think about her in years. Considering that it was Christmas, so Hogwarts was nearly empty, he didn't see the harm. He pointed his wand at the door and locked it. He sunk down, composed himself and closed his eyes.
"Lily Evans. Lily Evans." He imagined her eyes. Her emerald eyes that shone when she was happy, and dimmed when she was sad. He never really saw them without a sparkle, at least - before she met Potter. His fist clenched until the knuckles were white.
"Lily Evans. Lily Evans." He imagined her red hair, flying in the wind like fire. Yet, it was more beautiful than fire. More soft, more shiny, more free. He recalled one day in particular, her walking in the snow and her hair flying around her. Severus remembered how much he ached to stroke it. Severus leaned back in his chair. He had to stop. He was beginning to feel the raw ache in his chest, and the tears were beginning to flow.
"Lilly Evans! Lilly Evans! Lilly Evans!" His mind screamed at him. Severus cried out in agony at the name. Lilly! Lilly! Lilly! Her pale, beautiful skin, her radiant red hair, her beautiful emerald eyes, her perfect pink lips, her beautiful face, her perfect body, her sweet laugh, her gentle nature, her soft hands. Severus pushed the chair onto the floor and walked over to the window, staring out at the snow. He could still see the spot where James Potter had lifted him upside down and chortled. Where he called Lilly Evans, the girl he loved a mudblood. The day he lost her. Severus fell to the floor and hugged his knees, his breath coming out in ragged sobs. He missed her. He missed her every damned day of his miserable life. Every time he saw that stupid Potter boy, his heart ached. His eyes. He had Lilly's eyes. Not her lips though, those were his Father's. Hell, he wanted to punch those lips. Those lips that got to taste Lilly's lips. He almost had her. Severus laughed bitterly. No, he'd have never gotten her. A woman like her, so pure, so perfect could never belong to him. He weeped. Severus Snape sat, alone in his office and cried for Lilly. He cried through frustration, he cried because he hated James, he cried because he needed to protect Harry Potter, because he was Lilly's. He cried because Lilly would never know, and he cried because - after over 20 years, he was still in love with her. He needed her. He would give his life for her. He didn't want to live anymore, but he knew he had to. For Harry. His face crumpled, so he corrected himself in his mind.

"No. For my Lilly.