She'd be called away someday, of that he was fully aware. The few furtive glances he'd chanced against his better judgment, the way her name lingered on his half-parted lips, the time her robes had brushed against his, the halfhearted apology which never came—by then they'd known one another too well for that. And the certainty of it settled heavily in the pit of his stomach.
Potter would claim her in due course and that would be the end of it. He hadn't taken an active dislike to Potter until their second year, when his hold on her—tenuous at best to begin with—began to slip and her leaving seemed not so much a possibility as a foregone conclusion. It was then he'd developed the habit of taking his meals in the privacy of the empty common room; though she'd hated Potter he was nonetheless intent on gaining her favor, often seating himself beside her at the Great Hall and initiating loud, self-conscious discussions on Quidditch, whatever the house-elves had seen fit to serve for dinner that evening and—in the event that she prove particularly unresponsive—the countless shortcomings of Slytherin House. And Potter—he knew Potter's efforts would someday bear fruit, she could only defend him for so long—and by Seventh Year it had been too long and he'd sit in the dormitory with the shades drawn, the same pale, awkward little boy who'd stumbled at the Sorting ("Slytherin!" the Hat had crowed almost instantaneously; he'd had no time to protest, to tell it of the girl who was without doubt a Gryffindor, the girl who struggled to meet his eyes afterward across the banquet hall and fell somehow short) and continued to stumble ever since.
There was a time when—but Potter had to intervene, and though he knew it wasn't Potter he still put himself through the paces—loathing him, dodging his hexes, retaliating with his own, exchanging scathing remarks which ultimately came to nothing. In the furthest reaches of what passed as his memory, he knew Potter wasn't at fault. He'd simply assigned him the blame, tried to picture the two of them snickering behind his back, his arm around her waist, secure in their complicity—and found he couldn't.
Even at the last, when things had begun to unravel as he knew they must, even after he'd caught a glimpse of something dark against Lucius' pale forearm ("I went and did it, Severus—as befits a Malfoy,") and the Slytherins grown restless, she'd still nod at him when they happened across one another on the stairs. And he'd feel something grind itself slowly into dust in the hollow of his chest and knew someday he'd no longer be "Sev" but "Severus" even to her and as he himself took the Mark he knew he wouldn't ever be "Sev" to anyone again, but that was all right since she was gone and he'd wanted to cry out but bit his lip instead and couldn't speak for days.