This just came to me when I was listening to the song Fields of Gold by Sting. The story is not entirely based off the song but when I was listening to it for some reason I instantly got an image of a young Severus and Lily playing in a field together.
Severus remembers playing games in the fields with Lily, he remembers the way she would laugh at him as he chased her, her sweet voice calling "Come on Sev, catch me!"
He remembers the way her hair would fan out as she ran, the way her eyes would twinkle whenever she would catch him. He cannot help remembering the way she made him feel like he was the most important person in the world to her.
He remembers thinking how the sun, the heavens and everything around them should be jealous of their friendship. How jealous they should be that this wonderful and beautiful girl chose to spend her time with him.
He also remembers walking through the fields with her a couple of years later; he remembers longing to tell her how he felt about her. He remembers thinking how he loathes these feelings, how miserable she could easily make him feel. Yet he also remembers hoping that he'll never stop feeling this for her, he remembers how wonderful she could also make him feel.
He had wanted to reach out and grab her hand the whole time she had talked to him; he had wanted to kiss her there and then in the middle of their field of gold, he had wanted to hold her to himself and never let go.
He had watched as she ran through their field laughing as she held Potter's hand. He remembers being unable to look away as the fell down with him on top of her, as she reached up to kiss him.
Now, after her death, Severus looks upon the field where they had spent so much of their childhoods together. He wonders if she had ever thought of him, and if she had ever thought of their days spent in those fields of gold with the west wind blowing through their hair, and if she had done, were they memories she had cherished, or were they memories she had tried to suppress no matter what because she wishes that they had never happened.
Severus notices that there is a girl and a boy playing together in the field and the way the boy is trailing after the girl and hanging on her every word reminds Severus of himself when he was in these very fields with Lily and he cannot help silently wishing the boy more luck with the girl than he ever had with Lily.