Severus is gradually aware that he is not the only one in the nursery who grieves for Lily's death. A small boy sits in the crib, little tears streaking his pudgy face. The boy's eyes are trained on the strange dark man who is not his father, but still cries over his mother. Severus recognises those eyes, and it is only that recognition that makes him loosen his grip on Lily's body.
Lily's body slumps to the floor; she looks as if she's merely fallen asleep. Severus picks the boy up out of the crib, brushing the long, dark hair—hair that is clearly James'—out of those familiar green eyes. The little toddler cries, frightened by this stranger, and reaches a hand toward his mother. Severus shakes his head slowly and cradles the child against his chest.
Severus hears the front door swing open again, and there is a cry from the floor below; someone has found James. From the strangled "No!", Severus guesses it is Black or Lupin. Severus puts the boy back in his crib, taking in Lily's eyes for just another moment before turning to the woman on the floor.
Footsteps sound on the stairs. Tears flowing, Severus does something he has never done and will never do again; he kisses Lily's hair. It is only a brush of his lips on the red fire, but as he stands and Disapparates, his lips and eyes burn with memory and tears.