If I was trying to kill you you'd be dead is what he wants to say but that's not helpful in their situation and so he bites it back. Play nice. It's hard and it goes against everything he stands for but goddamn he has so little left here and he doesn't want to risk fucking that up too just because he can't be a decent semi-human being.
"That's not true." He starts, locking eyes with her. You shoved a soul in him. He has no choice but feel remorse, searing, burning, consuming remorse. Every moment, for as long as he lives. That's what a soul in a demon body does and it's surprisingly easy to muster up the words.