Severus could say, with all the certainty in the world, that love existed.
He knew, because that's how he felt about Lily. He had always felt it, and he would always feel it. What would be another explanation?
He knew he was capable of love, because he had loved her since she was just a little red-haired girl, with her green eyes and freckles, smiling at him.
Her red hair was now scattered on the floor where she lay, her eyes closed, her chest still.
Anyone looking from afar would say that what Severus was carrying was some kind of package, but it was all that was left of Lily. The tiny boy had his eyes closed, snuggled against Severus.
The Potions professor suppressed a tear. He had already cried too much. Careful so little Potter didn't fall, he bent down to leave one last kiss on Lily's forehead. He needed to let her go.
Then, with a sad sigh, he adjusted the baby in his arm and held him tighter to his chest. And he walked away, leaving behind the corpses of his enemy and the only woman he had ever loved.