It worked well for Severus Snape, this facade of disagreeability, the greasy hair and sallow skin and perpetual, sneering scowl. It kept his students at a safe distance, so there would be none left grieving when he came to the abrupt and messy end he was inevitably destined for. The life of a spy, especially one in Voldemort's strange ranks, was neither comfortable nor safe, and a favourite teacher in a place like Hogwarts often took on a role near to that of a parent. Much as Albus had been for him at one time.
He could not afford to put himself in that position, not for anyone.
So he resisted Poppy's attempts to properly heal his thrice-broken nose, leaving it hooked and crooked. He drank potions to keep his skin yellowed and unhealthy, his hair lank and greasy. He scowled and sneered, mocked and reviled, and tried very hard to slip careful measures of actual knowledge in between the insults and deductions of House points. In many cases, he failed at the last, but, always conscious of the precariousness of his position, he did try.
If he was occasionally lonely, if he sometimes wondered what it would be like to mentor a young mind or even have a civil conversation with someone other than Albus, well. It was a small price to pay for peace of mind, for the sure knowledge that no tears would be shed for him, that he was doing some good to make up for the foolish evils he'd perpetuated all his life. He hadn't so much gone bad as slipped and fallen into precisely the wrong company, and he was constantly grateful to Albus for lifting him up once again, for allowing him to be useful to the Light despite the ineradicable stain of Darkness he'd acquired.
Snape's disguise served him perfectly throughout Harry Potter's classes, until the fateful day he no longer had them, his Potions OWL falling below Professor Snape's exacting standards. Then, somehow, the boy spent the next two years getting over his foolish prejudices, and became damnably perceptive, a quality that would serve him well but not here, not now. Now, it was slowly destroying everything Snape had sacrificed to keep the boy safe, as he began to see the man hidden behind the masks.
"I brought tea, Professor, I noticed you weren't at dinner tonight," said Harry cheerfully one afternoon three short weeks from the end of his Seventh Year, setting a tray filled with an assortment of Snape's favourites, including the gentle waft of fine, strong Earl Grey tea.
"I don't see how my eating habits are any business of yours, Mr. Potter," said Snape with a scowl, hands tense on the edge of his desk.
"They're not," said Harry with a shrug. "But I thought you might look a bit healthier if you actually ate. Besides," he added, snagging a petit four from the tray, "This way I can have a bit of a snack, too."
"Why on earth would you want to share tea with me?" snapped out the involuntary, incredulous reply, even as Harry poured them both a cup, fixing Snape's exactly the way he preferred it. Snape felt a flash of anger at Potter's presumption, and tried not to think about what this small detail could mean, his analytical mind already extracting the essence of it and mixing it with other such nuances, leaving it to simmer while the conversation moved inexorably forward.
Harry shrugged again, a smile twinkling in his eyes. "You're not half so bad as you make yourself out to be. Occlumency aside, you're really quite kind when you think no one's looking."
Snape felt the building rage dissolve into fear as he leaned back into the chair. Even he was aware that his voice lacked its usual bite as he said tiredly, "You must be mistaking me for someone who cares, Mr. Potter."
"Nope. I've actually stopped mistaking you for someone who doesn't." Harry sipped his tea calmly, damnably. "Did you know that, fresh out of the bath, you're almost attractive?"
Snape was, unfortunately, very aware of that detail. Lucius Malfoy always forced him to bathe before their little trysts, tying his hair back with a leather thong and tracing whatever implement of torment he'd brought along over Snape's high, delicate cheekbones. "I don't believe your opinion on the matter is relevant, as you are not, in actual fact, the sort I'd ever want to attract."
That was, of course, a lie. Increasingly as Harry grew older, the thoughts that Snape filtered into the Pensieve before these lessons were of Harry's majority, Harry's bright green eyes filled with something resembling affection, Harry's naked body writhing beneath Snape's in a manner neither allowable nor healthy for the boy. Or himself; should Malfoy or, heaven forfend, Voldemort learn of such desires, he would find himself in a truly untenable position.
"Should've been more thorough with the Pensieve, then," said Harry. "I know what you think of me now, and very soon I'll no longer be anyone's student."
Snape shuddered, appalled at his own carelessness. "And what bearing, pray tell, does the end of your lamentable Hogwarts career have upon this entirely inappropriate conversation?"
Harry shrugged again, blushing slightly, and sipped his tea before answering. "Just didn't want you to be surprised when I showed up at your door, is all."
Snape closed his eyes, the cold fear roiling through him like seasickness. He knew his inability to resist such temptation had long been his weakest point. So, regrettably, did Malfoy and Voldemort. "Best have defeated the Dark Lord before then."
Harry set the cup down, and nodded. "All right. If that's your price."
Snape's eyes snapped open. "It was unwise of you to attempt to further penetrate my... disguise... before doing so. If He gets wind of this conversation, it will be used against us both."
Harry's gaze went from earnest to calculating in the space between heartbeats. Chips of cold, green ice winked out, and Snape shuddered again. "I don't think that's going to be allowed. Nor will you be keeping up this disguise once Voldemort's done for, unlike the last time."
Snape knew when he was defeated, he always did. Years of hiding had, after all, brought this one flaw into sharp relief -- his need to be loved, to be cherished, to belong to someone else. He bowed his head in acquiescence, unable to speak the words aloud. A gentle finger coursing down his cheekbone, an unconscious parody of Malfoy's dangerous caresses, was the only response.
It was enough.