A potential version of her didn't make it her, of that James was completely certain. But he knew well enough not to bicker over the little things that would make no difference. The point of things was that Lily was upset.
He blinked a little when she mentioned sleeping with Sirius. "What's so bad about that? I'd hardly mind if you did. I'd want to do it myself if he wasn't such a prat."
He was perfectly aware of the irony of him saying so.