Don't own anything of the Harry Potter Universe. This is suppose to takes place straight after the Harry's and Snape's last encounter in the Half Blood Prince
As Snape ran into the woods he couldn't help but throwing another look over his shoulder. His eyes went to the boy lying on the grass where he, only moments ago, had leaned over him. The insolent little brat had had the nerve to call him a coward. Him, who had just killed the most powerful wizard of all time, Him, who had deceived a whole world, who had sacrificed everything . . . And for what? All of Dumbledore's plans, that had put his life at stake so many times, had always revolved around this boy and yet when he looked at him, Snape felt nothing. His thoughts were interrupted by Draco calling for help. Snape grabbed the terrified boy's arm and continued away from the castle.
As soon as he had made sure that Draco was safe, at least for the time being, with a very grateful Narcissa, Snape went back to Spinner's End and collected the things he would need. He knew they would soon come looking and probably tear the place apart. He had to hurry. It wasn't much, almost everything could be replaced, he had learned over the years not to easily get attached. Attachment was a weakness that would always be used against you. So the only thing that was packed into his sack was some books and parchment scrolls. From one of the books fell a photo, as always it made him stop everything else, as always he couldn't handle it without looking at her, savor her.
A cute redheaded girl sitting in the grass looking up from a book, with a nice gentle smile and kind eyes, was looking straight at him and feelings of longing and despair mixed with the happiness of seeing her again rushed through him. He hadn't looked at it in months, not since he'd made the vow. With the task he had sworn to do and with every intention of keeping his promise, he hadn't felt like he deserved her smile, to look into her emerald eyes and enjoy the warmth he'd so often found there. Overwhelmed by the reunion he sat down in his worn velvet armchair.
"It's done and there is no going back" the words were blunt and cold and meant to stop thousands of thoughts, which had tormented his brain from the moment he had uttered the curse. For a moment he imagined that her eyes shifted from smiling to sad and reproaching. "Don't look at me like that" he half begged half ordered her "he demanded me to, I had to do it, for you" But as soon as those words had escaped his lips he turned the photo down and put it between two pages of the book he was yet to pack.
Had he really done it for her? For years he had done all sorts of things that Dumbledore had asked of him, in order to protect Harry, so that her sacrifice would not have been in vain, to do what she had died doing and now was unable to. But somewhere over time he had stopped questioning how the things he did helped her and Dumbledore's cause had become his own. He realized that Dumbledore had tricked him, had used Lily and her son as an excuse, all for his own greater plan, 'the greater good'.
But for some reason, this didn't upset him. This if anything should have made him feel something, but no. She wasn't the cause anymore, had never been Dumbledore's cause and a small part of him had known this, had been ok with it. Smoothly and discreetly she had been replaced by . . . he wasn't quite sure. But if she wasn't the cause anymore, then that meant that he had reduced her into nothing but a fading memory, a guiding star of the past but without power to affect the presence, she was truly dead. He had killed her.
Once again he picked up the picture and now the eyes had transformed into the clear understanding ones that had listen so many times before.
"There was a boy that I had to save. He's the same age as . . . I had promised to keep him safe, just like . . . Oh, Lily, please forgive me." He kissed the photo and without a second thought he took out his wand and made the smiling girl vanish. From here he was going to places where just bringing his own mind would give people enough reason to kill him and his chances of survival were slim. That he had managed to stay alive this long was a joke in itself. Now, all he asked for was a few more months, just enough time to complete the task Dumbledore had provided him with. He would fight the good fight, for whatever reason, to his death if necessary and frankly, that was the reward he was hoping for.
Just something that came to me. Thought about when Harry tells Voldemort that Snape wasn't his, but Dumbledore's. I don't think that's completely true, I think Snape was always Lily's no matter what side he fought for. That's my theory, what do you think?