Severus had shown the photograph to only two other living people - ever. Albus Dumbledore, when questioned as to his sudden 'change of heart' all those years ago, and Remus Lupin a few weeks after Albus' murder,
under almost identical circumstances. Yet he carried it with him, everywhere. Concealed so carefully within his clothing that no amount of searching, questioning, torturing, or other friendly activities among his Death Eater associates had ever come across it - though it certainly suffered more creases and the occasional stain he'd been unable to remove from such activities.
It had arrived in one of the last letters she'd ever sent to him. Out of dozens of letters she sent after they finished school - all of them always unanswered, and now forever more unable to be answered. She had never stopped believing in his 'goodness', that he would 'come back' from the path he had taken, the choices he had made, and had never given up on him, in spite of their rocky history.
He had not loved her. Not in a romantic sense. She was far too good to be loved. Yet she was real. She was sweet and kind and funny and beautiful and willing to scream right back at him when they fought, when he was wrong.
She'd held a higher belief of himself than he could ever live up to. Yet, it had been that faith, in the end, which made him want to make the effort.
It was fear of her death, the desperate wish to save her from his own horrid, wretched mistake, which had brought him literally crawling back to Albus Dumbledore when he was just twenty years of age.
It was her image, and the promise she had asked of him, the promise he had never seen her again to be able to answer in person, which had driven him all these years.
And the photo never left him.
Her final message to him was inscribed on the back in her neat, feminine writing, the ink also beginning to blur and fade:
Severus, I knew you weren't one of them! Not really. Not in your heart. We’re safe. Albus warned us and we’ve gone to hiding. I won’t say how or where, but rest easy that we’re safe. Sirius helped us… I had wanted to ask Remus, but you know how close James and Sirius are. We haven’t seen Remus in quite some time.
Don’t worry over me. I have to fight, you know that. I’m not afraid. But if the worst should happen… please, for the sake of our friendship… watch over my son? Always your friend, Lily