Warning: Dumbledore isn't very nice in this! I don't often write him like this, but after the relationship he seemed to have with Snape in DH, I thought I'd experiment with it. Please let me know what you think!
A Bitter Brew
"You cannot be serious, Dumbledore!" Severus Snape spat as he paced the Headmaster's office furiously, bitter thoughts swarming through his system. "Are you stupid, old man? How could you even think of making this decision?"
Albus Dumbledore sat behind his desk, his eyes twinkling serenely as he stared at his livid Potions Master. Snape wanted to shake the man's shoulders in his rage and betrayal. It seemed that whatever Snape did, however hard he tried to obey the man before him, Dumbledore only worked out more ways to make his life a living hell. Wasn't it bad enough that he had been made to work at the school he now hated with all his being? Wasn't it bad enough that every single dratted day, he had to face the reincarnation of his worst enemy, who had the eyes of the only person he had ever loved? James Potter had stolen Lily from him, and Snape had to face that fact every single day when he looked into the eyes of the pathetic, moronic little boy. Potter had received recognition for finishing the Dark Lord, when all along it had been her, her who had loved the little whelp who had done nothing for her but breathe. Why did the brat deserve her love and not Severus?
And now, Dumbledore was foisting this upon him. Not only was Remus Lupin coming to Hogwarts to fill the Defense Against the Dark Arts position, which was what Snape had always wanted to teach, but he was also being required to make the Wolfsbane Potion for the monster, the monster which had once tried to kill him. His little cohort, Black, had set Snape up to be slaughtered, to be nothing more than common trash. And Dumbledore had done nothing about it; he'd just sat and twinkled and taken a few house points from Gryffindor, at the same time threatening Snape with expulsion if he told of the mongrel's condition. And now Severus was expected to sit back and do nothing while that half-breed was welcomed back to Hogwarts with open arms.
"Black is on the loose!" Snape roared, losing control for the first time in a long, long while. Spittle was flying from his mouth, and his hands were clenched into fists while his whole body trembled. "And Lupin will abet his crimes just like he did in school! Thank you very much, Headmaster, for proving once again that the house of Slytherin means nothing to you. Your blessed crop of Gryffindor bullies can do no wrong! Do you not realize, Headmaster," he snarled, injecting as much disrespect as he could into the three-syllabled word, "that Black killed thirteen people, including that pathetic Pettigrew? Do you not care for the safety of your sainted Harry Potter? Black will murder him without a second thought, and his pet wolf will join him, and ..."
"That's enough, Severus!" Dumbledore said sharply, his eyes turning to slits of icy blue. Gone was the grandfatherly appearance Dumbledore gave off to so many students, gone was the kindness, the caring in his demeanor. "Almost twelve years have passed since you promised me your loyalty. Do you really want to go back on that now?" His voice becoming dangerously soft, he continued, "You owe me, Severus. And you owe Lily."
Snape made a long, strangled noise in his throat as the dreaded name was said. Every time he got in an argument with the Headmaster, it always came back to her. He knew he had done wrong by her ... Merlin, he'd known it ever since he had come across her pale, lifeless body in Godric's Hollow, and even before that, when he'd relayed that thrice-damned prophecy to the Dark Lord. "Do not bring her into this," he growled, grief and rage roiling through his veins.
"And why not, Severus?" Dumbledore demanded, his eyes still chips of ice. "You promised that you would do all you could to rectify your mistake. Remus Lupin is coming to Hogwarts. That is a fact, and you cannot convince me otherwise."
"Fine!" snarled Snape, beginning to hyperventilate as he collapsed into the chair across from Dumbledore's. "Fine! But you will see, Dumbledore, you will see that your decision will be one you'll regret! Or maybe not. Lupin will pander to Potter, he will let him get away with anything, and that will make you proud, will it not?" he wheezed, his head pounding.
But Dumbledore did not speak again. Snape was deeply infuriated at how he still sat calmly in his chair, staring at him unblinkingly. Severus hated how the man had so much control over him. All he had to do was bring up Lily, bring up what he had promised him in his state of grief and denial right after her death. He remembered with crystal clear clarity finding her body, staring into her lifeless emeralds, tears falling on her beautiful, fearful face ... she must have died hating, despising him. That thought alone tormented him every night, and he sometimes had to put a Silencing Charm on his private quarters so others would not hear the fierce, despairing howls that emenated from him after a nightmare of her prone body.
And it was a bitter brew to swallow indeed as later that night, Professor Severus Snape lay in bed again, knowing that he had accepted that one of his worst tormentors, one of the people who had helped his and Lily's friendship disintegrate into tiny shards, was returning to Hogwarts. The only thing that comforted him, however, was the thought that come year's end, he might be destroyed, just as Lockhart and Quirell had been.
And to Snape, it would be good riddence indeed.