At first Faith was confused before the realization dawned. "The vigilante, it was you." And Ruby both. Suddenly those things the demon had said made a lot more sense. He'd been set up. Probably had something way too valuable to lose that he offered his own life to protect it. Family maybe?
"You weren't checking to see if they were evil or not."
Her first reaction was to try to blame Ruby for it all, believe that it had all been her idea, her responsibility. That she'd just led Sam down this path. But ultimately, did it make much difference?
"Power like that," she eventually forced out, after a long silence. "It can mess with your mind, make you feel better than everyone else, like you have the right to pass judgment on them all."
She made herself look up at him, some guilt clear in her eyes. "I should have seen it. Should have figured it out sooner. God, it was right in front of me and I didn't even see it, some Slayer I am."