It's an overflow, the moment. The Self-Shuffling card house tumbling to the ground; the Patronus disintegrating when a happy thought wears out. He feels like he's sitting in sixth year Muggle Studies—the awkward science year before mathematics, after culture—like he's sitting there in Muggle Studies, Burbage babbling on about a supersaturated solution not holding out when another drop of solute's added in. This moment is the solute, and this moment's the dementor, and this moment's the top card that snaps.
He really is becoming a bit of a nerd. James Potter, Head Boy, quoting chemistry easily; always so quick with a quill. It's like he's losing himself in this madness and maturity, forgetting his place with the coming of age, the war. Everything comes back to Voldemort's reign, when your place is a point on the circle of life; one-eighty degrees from evil is a parallel vector. The solution is simmering beyond its capacity, but it takes but one drop (but one death) to come crashing.
It's an overflow, the moment, even public like this. The common room is crowded and rowdy and loud; he's hateful, but thankful, once off to the side. He's losing the life he's so carefully crafting: it slips through his fingers, alongside the letter so marked by the Ministry seal. His breakdown is private, silent but wild, burned into the rhythm, the cadence and flow, of his thoughts that are raging and maniac around and again—
"You're all right?"
He glances up, startled, reflected in a gasp. Vaguely, he registers Evans (got a letter yesterday), but he can't quit his musing. He stammers a while, meaning gone from his eyes, and his heartbreak is pulsing; his mind won't break pacing for the sake of conversation; he's fading—
A hot slap to the cheek interrupts.
James Potter gapes, somewhat stunned. It's Lily Evans he's talking about, poster girl for properness, ever sentimental and kind. She seems mortified, ashamed, and can't help but wince when she says, "I'm sorry; you didn't deserve that, not in the least. But Remus told me you didn't take the news well—about your mother, I mean—and I've never been articulate, and, well, someone needed to snap you out of it—"
"Don't bother trying," he says shortly, and breathes. And she knows, understands, and they're locked up together, just Lily and James in the corner's slight shadows, locked up together away from the action and equally locked up inside.
"It's funny, you know?" Lily sighs. "To think we're at school, sheltered, completely okay, when out there wizards are dying, and you think that you care. But you don't till you do, because you know that it's awful, but a few little footnotes in history won't break you, not really."
He finishes her thought: you don't care till you do, and then the façade's caving in around you, and you realize you've been blazing mad from the start; the anger's just falling in place. Oh so funny to think that someday it'll be you: people telling the story of Lily and James (how they loved and they fought and they fell) like they know you, when really, you're all on your own. Almost makes him want to write this all down, when it hits in this moment.
When all he can do is study and sit, maybe take Lily's hand in his own, and become one with the casualties.