Severus looks at her and believes her, and that's clear in the way he stares. Words fail him; who would know what to say, here. Hell if he has any idea. He loves Lily like nothing else. She's the only person he's ever felt truly accepted by, and he didn't realize it until it was too late. Of course he'll accept whatever he can get from her, even if it's breadcrumbs.

Something bothers him, though. It starts as a tiny bubble of a thought, not even fully formed, but it won't leave him alone.

"Why did..." no, that's not right. Severus tilts his head, trying to sort out his phrasing. "Under what circumstances would he even need to make that kind of promise?"

What in the fuck was she trading on, for something like that to come up.