Well, fuck. Terrence had done a decent job of rationalizing away any guilt he'd felt, but it was coming back. He didn't feel guilty for killing anyone, not even his parents, didn't feel guilty for being a turncoat, but he felt guilty for this.
"I'm sorry," he said, and he meant it. He gave her a tiny, wry smile. "I honestly thought you'd be better off being able to think for yourself. But I won't even bother pretending that I wasn't selfishly motivated, too." He sighed, and lifted a hand to run it through his hair. "Ella helped me get rid of the - fog. It was a good thing, for me, and it drives me insane to see people walking around all --" He made a gesture that encompassed the entire problem, and left the sentence hanging.
Was there a point in arguing that she wasn't alone, that she could trust him? Probably not. She would either trust him again, or she wouldn't. Her trust in him wouldn't be misplaced, but he wasn't going to help things by insisting that he was trustworthy.