"Severus, you are too hard on yourself, and you give me far too much credit. My continued presence at Hogwarts may have forestalled some of the anguish the Wizarding world is experiencing, but it has been your actions that have allowed us to proceed as far as we have. My regret is that you have by necessity been so alone in your endeavour. It was never my intention to leave you without friends, Severus. I can only hope that we are nearing the end."
"The end?! And what will that end be? Will there be anything left of the world we know?"
"Because of you, we can maintain hope that we will save our world."
Severus turned away from the portrait in disgust. "It was because of me that this whole thing started."
"No." Dumbledore was emphatic. "You played a part, certainly, as did we all. But you cannot know what would have happened had you taken different actions. You must not continue to blame yourself for a past that cannot be changed. It is only what you choose to do now that matters."
"What I choose to do?! I have no choices! I am completely at the mercy of the Master I chose to serve when I thought I had no other choice. Choices! My choices were taken away the moment I was Sorted into Slytherin."
"You are wrong, Severus. You still had choices. Yet I understand your resentment. You believe that your life would have been different if you had been Sorted into Gryffindor with Lily. And indeed it would have been. But not necessarily in the way that you think. Where would we all be if you had not been here to protect Harry all these years?"
Severus cursed. "And where has that got us? No one knows where he is or what he's doing. The Dark Lord grows stronger and more confident every day."
"Have faith, Severus. Harry will do what needs to be done when it is time. And you will know what to do as well. As for your choices, well, I suggest you ask the Sorting Hat why it placed you as it did. It may give you a new perspective."
"Ask the Sorting Hat? Are you daft? I will not consult an article of clothing for advice. And you said yourself that perhaps we Sorted too soon. What help can the wretched Hat be now?"
"Well, it is your choice, of course, Severus. But you may find it enlightening." Dumbledore closed his eyes, and Severus knew that the conversation was over.
Against his will, Severus glanced over at the shelf that held the Sorting Hat. Was the blasted thing winking at him? He strode across the room and snatched the Sorting Hat from its shelf. Feeling utterly foolish, but unable to resist the compulsion, he placed it upon his head and sat down in the closest chair.
"Ah, Severus Snape. A very difficult one to place." Severus sighed as the Hat continued, "Truly, you would have done well in any House." Severus doubted that; he was born to be in Slytherin. Hadn't his mother taught him that all his young life? "Oh, but your mother underestimated you, as have most of the people who have known you. But there have been those who saw beyond your greasy-haired, surly facade." Severus was surprised at that; how did the Sorting Hat know what he looked like?
"Ravenclaw would have suited your intelligence. You know you have always been years beyond your peers in that area. The challenge of competing with others of advanced intelligence would have kept you working for approval. Yes, you would have done well in Ravenclaw." These words did not surprise Severus; he was no braggart, but he knew his intellect was advanced. The Sorting Hat's next words, however, made him scoff.
"Hufflepuff would also have been a good fit for you." Severus released an audible sigh of disbelief. He was hardly Hufflepuff material. "You do not appreciate the value of Hufflepuff traits; the members of that House should be revered, not mocked. One of your greatest assets is your stubbornness; you do not give up until you have accomplished your goal. And once you have chosen where to confer your loyalties, your will does not waver." Severus did not miss the slight emphasis on the word chosen. "True loyalty comes from respect, not fear, and your comprehension of the difference has been both your downfall and your salvation. Hufflepuff would have taught you to appreciate your innate instincts rather than to fight them." Why then had the Sorting Hat not placed him in Hufflepuff? Could he have avoided all the heartache and regret that filled his life? There was no time to consider that possibility now; the Sorting Hat was continuing.
"Gryffindor might seem the logical choice to those who know of your deeds this last decade and a half." Indeed, Dumbledore himself had implied that Severus's courage would have suited him for Gryffindor. "It would be nearly impossible to find a wizard who has displayed more courage in these dark times. Oh, anyone can make a stand on the spot; who wouldn't protect his or her child when faced with immediate danger? No, true courage is revealed in the choices we make every single day. Godric Gryffindor would have been proud to consider Severus Snape as one of his own."
Severus was stricken. If he was so brave, why was he not placed in Gryffindor? Why was he placed among the snakes, to be further corrupted and used? If he had not been surrounded by future Death Eaters, would he have followed that path? Would he have been able to thwart the Dark Lord as a member of the original Order of ...?
"Slytherin was your heart's desire." The Sorting Hat interrupted Severus's train of thought, and he immediately switched tracks. His heart's desire, indeed. He was all of eleven years old, for Merlin's sake! What did his heart know? "Your heart knows your true place from the moment you are born, Severus. It just takes your mind longer to sort it out. Slytherin was a good fit for you. You were ambitious, eager for recognition, desperate to prove your worth. These attributes can lead to great success, but they also have dangerous side effects. In a different time, perhaps, your chosen path might have led to greatness. As it was, your role was less rewarding." Less rewarding? Was that what the Sorting Hat called it? Being a pawn was "less rewarding" than being a hero? "Heroism, Severus, does not always accompany fame. Where would we be if you had not reported the prophecy to Lord Voldemort? What would have happened if Lily had not been given the choice to live? If not for Lily's son, what motivation would you have had to fight Lord Voldemort? Severus Snape, you were Sorted into Slytherin not only because you chose to be there but also because you were needed there. Yes, you would have done well in any House, but where would the world be now?"
Severus was dumbfounded. He had never truly considered how things would have been different had he not delivered the prophecy to the Dark Lord, had he not appealed to Dumbledore to protect Lily Potter, had he not begged the Dark Lord to spare her. If he had never become a Death Eater, he could never have become a spy for the Order....
Severus winced as the Mark on his arm seared. He gasped as the meaning became clear. Potter was here? In the castle?
Accepting now what he knew he had to do, Severus returned the Sorting Hat to its place on the shelf and descended the moving staircase for what he knew was the last time. He could not bring himself to look at the portrait of the man who had manipulated so many people for so many years, but as the door closed behind him, he whispered, "Goodbye, Albus." Then he set out purposefully to find the boy--no, the man--who could finally end all this misery.
Notes: I noticed that in the series, Severus never addresses Dumbledore as Albus. This really bothered me, so I threw in the final goodbye as a sign that Snape and Dumbledore are now equals.