A.N. Hey all! So here is another new Harry Potter story. I wrote it as part of a Facebook fanfiction competition (run by Admin Bellatrix, from the page 'No part of your body has permission to be in Hogsmeade" Severus Snape'). I fiddled with the timeline a tiny bit here. In this story, Severus started working as the Potions Master at Hogwarts when he was twenty—the age that he, Lily and James are in this story. Lily and James are expecting Harry. Lily has gone into hiding, because she's a member of the Order of the Phoenix and is therefore a target. However, no one knows about the prophecy yet.
For the seventh night in a row, Severus glided down the corridor like one of the many ghosts that haunted the hallways of Hogwarts. His heart was racing, his palms were sweaty. Without knowing it, his stride quickened until he reached the small door in one of the annexes on the second floor.
And there it was. The Mirror of Erised.
Severus sat before it, his robes billowing out behind him in their usual dramatic fashion. When he had first found the mirror, he had closely examined the delicate frame, the inscription, the glass, the feet. Now, all he cared about was the images that it would show him.
There she was—his beautiful Lily. Laughing, smiling, casting spells, brushing her dark red hair. And always looking out with those beautiful green eyes that always glinted like the sun off a perfectly cut emerald. She always looked happy in the mirror, never angry or betrayed like the last time that they had spoken. He reached forward to cup her cheek, to stroke her hair, but his hands only met smooth glass. Severus bit back a sound halfway between sorrow and frustration, and then wrenched himself away as he did every night. As he resumed his patrol of the corridor, hoping to stop the mischief of teenagers that were only a few years younger than he was, he swore to himself: he had to find Lily. He had to make the scene in the mirror come true.
—Line Break—
It took Severus months to find Lily. With his new job as the Potions Master at Hogwarts and his tasks for the Dark Lord, Severus rarely had much time for himself. In addition, Lily had gone into hiding with the birth of her son so near, while her idiot husband kept running around, presenting an irresistible target to the Dark Lord. For a while, Severus was worried that he would never find her.
And then one day, while shopping in the apothecary in Diagon Ally, he saw her outside. Her hair was pulled away from her face into a long braid. Her eyes sparkled in joy as she talked to Potter, her entire face lit up with excitement as they walked together. She delicately maneuvered herself around merchants, peddlers and other obstructions. Her left hand was clasped in Potter's, but her other arm was gently wrapped around her very pregnant belly. Suddenly, her expression brightened, and she pulled Potter over to a stand of baby clothes. Severus steeled himself to approach her.
And then he stopped
The image of Lily in the Mirror of Erised…this was it. It wasn't Lily forgiving him. It wasn't Lily leaving Potter to re-join him at Hogwarts. It wasn't even them talking to each other. It was just Lily happy. Severus looked at her again, ignoring his own emotions, calculating instead of feeling. Lily was happy. She was leaning in to Potter's side as they looked through the racks, looking up into his face with those beautiful eyes of hers. And in that moment, Potter leant down to gently kiss her, his own hand joining hers to rub her stomach.
For an instant, the pain was too much for Severus to bear. But it was a bittersweet pain now instead of pure agony. Severus looked on at the happy couple, and finally acknowledged to himself that if he were to approach, Lily would cease to be happy. His presence, which used to bring her joy, now only brought her pain. So Severus bowed his head to the un-seeing happy couple, and backed away.
"Goodbye, Lily," he said to himself, and then he was gone.