"I told you." Remus' eyes narrowed as he pulled his hand from Sirius, speaking the words very slowly. "There was a traitor in the Order. He sold us out."
Seeing Sirius' obvious distress, Remus sighed. It was something that had never made sense to him. Remus had always felt like he was closer to Sirius than he was James or Peter. Sure, Sirius was closer to James. But, that was only to be expected. So, why hadn't Remus sensed the betrayal? Why, even with as little as they'd seen of each other in that last year, hadn't he sensed any of this, with all the gifts of his condition he'd been learning to hone, how had Sirius been able to keep this from Remus?
"There was a prophecy about a child born that would defeat Voldemort. James and Lily were expecting. If I remember correctly, you've only come from a few weeks before they announced it. Frank and Alice were expecting, too. We didn't know which child, so they all went into hiding. Lily and Alice both gave birth that summer. With no way to know which child was the target, plans were made to protect both. Worked for awhile. But, we became aware someone in the Order was passing information to the other side, maybe for a long time. James wanted to have the fideleus cast on the house."
He wasn't avoiding Sirius' gaze now. Instead he was actively watching his once upon a time friend for any sign, any indication, that might give away the truth of the other's heart. It was possible this Sirius hadn't started to turn, yet. "Within a week after it was cast, Voldemort showed up at their house. Killed James. Killed Lily. You were their secret keeper, Sirius."