As soon as Regulus said the name Greyback, Remus could feel himself tense. But, he did as he'd been asked and just listened because he could see this was difficult for the other man to say, whatever it was going to be.
This was the most open Regulus had ever been about his past and Remus could only nod as he listened to the choices that had taken him to the Death Eaters in the beginning. That part, Remus could understand. Had Remus found friends who sided with Voldemort instead of Dumbledore, it was easy to see himself following them into the ranks.
Nor did he shy away from the admission about enjoying it. Remus knew that as well, he knew what it felt like to relish it, even. It was part of his nature he fought against, but still part of his nature.
But, the rest...
His eyes closed as soon as Regulus said 'Wales', everything inside him gone cold with dread of what was coming, but he forced himself to open them and listen to the rest of Regulus had to say.
To feel pain he didn't think even undergoing Cruciatus during a transformation could match.
He'd thought about the possibility once, but how much of a coincidence would that have been? He'd dismissed it, not truly wanting to know the answer. Happy to leave that one question he would never ask his lover.
His lover. The man who'd dealt the killing blow to his father and watched as his mother was brutalised.
When Regulus finished, Remus couldn't speak. Words hadn't been invented for the clash of emotions threatening to tear him apart in that moment. Gods, he couldn't breathe. He had to get up, wrap a blanket around himself because he felt too raw and exposed.
But, he didn't leave. He'd promised not to leave. And a large part of him still didn't want to, though he didn't know what he did want to do.
Eventually, after standing, silent and unsure for a long moment, he merely sank to his knees, much as he had that night when he'd walked into his childhood home to find blood and death. "You weren't ever going to tell me, were you?" he asked, voice barely a whisper through tears he refused to shed. It wasn't really a question, though. He could see the answer well enough.
"I was late. I'd been out on a mission with Moody and we were late."