Severus could remember the first time he noticed it. It was in the third year, before the animosity between Lily Evans and James Potter had begun to explode in earnest. He'd been taunting her again, this time for her extensively color-coded transfiguration notes with key vocabulary terms bolded and charmed to recite their own definitions. To Severus, it was classic Lily Evans—adorable, glowing resourcefulness, his admiration for which tied his stomach in knots. To Potter, it was the joke of the term, something to double over laughing about. Severus had just been thinking of how much he hated Potter's face when he laughed, when he caught sight of Lily's face. Nausea struck him instantly.

Lily, like most sensible witches and wizards who got anywhere near Potter and his madcap gang, had learned to ignore most of their pointless gags and inability to get through a single lesson without some childish distraction or other. Lily could often be seen casting the group her trademark withering glance, or glaring furiously in their direction when their horseplay began to drown out a particularly interesting part of a lesson. Sometimes she'd ignore them completely, and rarely—Severus could not help clenching all over at the thought of it—she'd crack an involuntary smile, then hurry to suppress it, her rosy cheeks giving her away.

This time though, with her magnificent notes before her, Lily did not ignore them, nor glare, nor smile. She was red all over, the corners of her mouth drawn back, and Severus did not need to see the tears sparkling in her brilliant greens eyes to know she was trying her hardest not to cry. And although Pettigrew and Lupin were unabashedly amused, and although Black laughed hardest of all, Lily was fixated on Potter. Though they never spoke of it again after Lily stormed from the classroom, for a while Severus noticed the incident still clinging to the air. And it was not Black, Pettigrew, or Lupin who had earned Lily's silent treatment. Potter alone had earned that, and it was him she fixed with a look of betrayal every time he spoke for the next few weeks.

Betrayal of what?, Severus tortured himself wondering. Potter was nothing to her, surely. And although Potter certainly liked to occupy himself with Lily, she was not everything to him as she was to Severus.

There were other moments over the next couple of terms: was she checking her reflection in that tiny compact because Potter had walked in, or would she have done that anyway? Did she do that when Severus walked into a room? He would have to try to make a note of it next time. Why was Potter handing her a book between lessons? Was it a schoolbook? Why was she accepting it instead of cursing him into oblivion for daring to speak to her, to share the same air as her? Was that a smile? What conversation had led to this? Why had she been sitting directly next to him in the booth the Gryffindor fifth years all shared at the Three Broomsticks?

She had scolded him more than once now for his nosiness. "You're not my keeper, Severus," she'd remind him, half sing-song, half weary. Every day she seemed less interested in supplementing their voluminous masterpiece, The Many and Varied Facets of James Potter's Awfulness. But it was difficult for him to stay angry with her over this; there was so much more to him than hating James Potter, after all. And she was everything to him.

Severus believed he'd find a way back into her good graces after she tried to end their friendship. How could they not make it work? Severus could hardly remember a time before they were friends. How could they live without each other?

Of course, it had been difficult walking in to see Lily embracing Potter in the Entrance Hall on the last day of term. Embracing him, of all things. But it was as she had said: his father had just died. She was doing what she would have done for anyone. It was only the smallest fraction, surely, of what she would have done had Severus been experiencing some crisis. Hadn't Lily been sympathetic even when Avery's mother had fallen ill? And Severus knew with certainty that she hated Avery. She could show sympathy to Potter and still hate him. Severus was sure of it.

The moments came more frequently after that. And the more it hurt, the more it stirred his guts, the harder it was for Severus to look away, to stop watching them out of the corner of his eye. But Lily, Eaton, Longbottom, Warren, Black, Jacobs, Lupin, Pettigrew—they all ran in the same circle. It wasn't about Potter. She didn't want Potter. He didn't have to think about Potter. A pair of siblings don't take up together just because they're forced together all the time, do they? They were from the same Hogwarts House and there was some obligation to get along, that was all.

It was a stormy autumn evening during their sixth year when the cracks in his certainty came dangerously near the foundation. It wasn't the misty sort of rain they had grown used to. The storm was booming, the rain battered the ground like bullets, thunder roared at the heavens. It was the kind of evening Severus and Lily would sometimes spend hidden in the Astronomy tower, leaning against the stone column in peaceful awe of the storm.

This night, however, was the second meeting of the Dueling Club's advanced section. Severus knew why the teachers and Head Students had wanted to start the club, but he found these meetings ridiculous; learning safe magic in the Great Hall would be about as useful in the face of the Dark Lord as offering him tea and cakes. He'd come out on top against his first few opponents, and was not careful, as Lucius had warned him to be all those years ago, about drawing attention to himself. He knew there were few students at the school, even in the seventh year, who could produce such advanced magic or do more crafty battle than he. And thanks to Potter and his band of imbeciles, he had had a lot of practice.

Bored, he cycled through his assigned opponents, waiting for the night to be over, when he heard Professor Slughorn shouting delightedly at something. Severus rolled his eyes—what a feeble excuse for a Slytherin Head of House.

Severus wordlessly held his current enemy in a bodybind curse while glancing in the direction of the commotion. He saw a flash of long, dark red hair and vaguely registered that Slughorn was—who could believe it?—fawning over Lily Evans. How novel indeed. Severus made to turn back to his unfortunate opponent again, but something stirred in his stomach; Lily and Potter were dueling.

But surely "dueling" could not be the word for what they were doing. Severus turned fully to see them now, as many of the other students had begun doing, their own battles forgotten. Lily's face was pure determination—flushed, stony determination. But as she wiped away the hair pasted across her damp cheeks and forehead and readied herself to hurl the next jinx, Severus saw something else in her expression, illuminated now and again by blasts of lightning, and when he glanced at Potter's face he found it there too: like thirst, if thirst could burn hot all over.

Severus had seen them duel before. Potter would make some idiotic self-important remark about how he wouldn't want to use the full force of one of his spells on her, and Lily would laugh acidly, daring him. But now Potter had rid himself of his obnoxious gallantry, it was clear. A smile underlined his fierce expression, but there was fierceness nonetheless. He was hurling his heart and soul into this fight, and Lily was meeting it, hex for hex, curse for curse, besting him, forcing Potter to see not a woman that needed to be looked after, but a force to be reckoned with.

Yes, they were dueling. But they were playing too.

There was a collective gasp from the Hall as Lily shouted a curse, and as the thunder echoed her incantation, Potter rose from the ground and was pinned, wandless, against the stone wall. His eyes widened as hands—enchanted stone hands—grew like weeds from the wall behind him and held him there. Aghast, his eyes darted to Lily's triumphant face, then to his wand on the floor beside him. He extended his arm, reaching for it, looking almost childish, as though about to throw a tantrum about his wand being on the floor instead of in his hand where he wanted it. He closed his eyes, and as his eyebrows knit together in what looked like pain, Severus was elated beyond belief—was Potter about to cry?

But then, to cheers from the crowd that made Severus want to be sick, Potter's wand zoomed into his outstretched hand. Exhausted from the effort, he barely managed to free himself. But when he did, he and Lily shook hands, Slughorn declaring a victory for Lily, and Lily calling it a draw. They were laughing together for far too long, and shaking hands for far too long, and looking at one another for even longer—who could stand to gaze so entirely at another person this way?—as if the long-awaited answer to some life-altering mystery was written there. Severus hated to watch, yet he could not stop himself.

This, however, was not the moment he knew. It was not even when she said the words to him, clinging to Potter's loathsome bloody body after he and Severus had fought. He came to know the truth in many little moments, what felt like hundreds of recurrences of the same little reflexive ritual between them, which over time would become one memory in Severus's mind. He would always remember the first time it happened: in Potions class one warm afternoon, Slughorn had bent over and smashed an entire rack of crystal vials onto the floor with his rear end, and Lily and Potter turned to look at one another in unison, poorly suppressing their glee. Most of the class had erupted in giggles, it was true. But it was as though all the laughter in the world was reserved for Lily and Potter. It was the same when Professor Binns told the story of Donald Arcy; Potter's eyes fell on Lily's like an instinct, and in concert they looked away, a silent agreement that if they looked at one another any longer they would burst. It was always Potter Lily sought when she felt about to explode with mirth, and more and more they seemed unable to laugh, to enjoy any moment of absurdity or irony, without looking at one another. It was the way to laugh, Severus thought, when there was someone in the room who meant everything to you.

But Lily had kissed Severus. Hadn't that meant anything? She had pressed her lips to his, albeit years ago, and made him feel as though nothing could ever go wrong in his life again. There must be a way to stop Lily going down this route, to head her off at the pass and prove that he was the one she should be with. She should be his, not Potter's, and he had been there first, known her first, loved her first. He knew now that he should have acted more quickly after they kissed, known what to do, handled it more coolly. Instead he'd been awkward, uncertain, afraid, waiting for her to pounce again in case the first time was just a dream. But the day never came, and she seemed to forget it had ever happened. But she couldn't have forgotten. They had kissed. It was everything.

He understood the truth the first time he saw them kissing. He was pacing the grounds one autumn afternoon, rounding the lake and planning how he would approach her, convince her. Maybe it could be as simple as asking her to visit Hogsmeade with him. Maybe it would all take off from there. Maybe she would kiss him again. And this time, he would know what to do.

His stomach dropped out the moment he spotted them. His knees shook. His throat closed. Little lights burst before his eyes. He was going to pass out.

She was clutching him as though she'd die if they let go. Severus felt a piece of himself disappear as he watched Potter touch her hair, cup her face, taste her lips, drink her in, melt into an altogether different version of James Potter than anyone had ever known, a James Potter that existed only when kissing Lily Evans on a cool fall afternoon by the lake, leaves caught in their hair.

Severus crumbled under sickening fury, wishing he could shut out the screaming in his own head, telling him one moment that everything about this was wrong and that he should storm over there and rip them apart, the next moment telling him that everything about this was right.

Because now he understood that this was a kiss. And what they had done in the fourth year was not a kiss, but an experiment conducted by Lily Evans in her pubescent curiosity, the results of which had no bearing whatsoever on their relationship. There would be no other experiments.

And he could not rush over and pry them apart. He would regain his balance, hold onto this oak tree until he steadied himself, and walk back to the castle. Lily wanted to kiss Potter. The truth was in every move she made, every touch, even in the arch of her eyebrows. And what Lily wanted, Severus must accept. Because she was everything to him.