Avarice: 1) jealousy. 2) excessive or insatiable desire or greed.
It's the way she looks at him.
Lily's green eyes sparkling, she punches James Potter, and Severus inhales triumphantly, but it's only play, and her fingers linger on his arm.
It's the comfortable brushing of their shoulders as they study side by side. It's their laughter, Lily's so shameless and joyful, throwing back her head, lips full of shining teeth. It's James Potter pushing his pathetic glasses up his nose, watching her, drinking her, every breath she takes igniting the smugness in him at finally owning her.
Severus watches from a distance, watching Potter watching Lily. His Lily. They kiss, and Severus feels his white-knuckled fingers tighten on the doorframe.
Potter. The name is spat on the floor as Severus stalks down corridors. Potter in his angry, clicking footsteps on the stone, Potter in his unfortunate heartbeat.
It's their love.
Hatred. Anathema. Odium. Rancor. Antipathy. Acrimony. Loathing.
There are so many words for hate, and only one word for love.
And it's in the clench of Severus's hand, his narrow eye under his fringe, lurking around the corner to catch a glimpse of Lily, as mid-laugh she looks up at him, half hiding reluctantly in the shadow. His shame at spying heats his ears and his skin around the collar, stupid stupid stupid. Lily looks at him, and a hint of something automatic kindles in her face, delighted. Then she blinks and the momentary smile-flicker vanishes. It takes with it a piece of Severus's heart.
He turns from her gaze and doesn't stop running until he trips and falls.
It's the way she looks at him.