"Uh-huh," he grunts, still skeptical. Maybe she's playing them both like a fiddle, but the thing that's making Dean not quite sure is that there'd be no reason to up the ante about that here, now. All she needs to do to keep Dean from wanting to gank her is to behave herself; they'd already established that, even. Why pretend like she's in love with Cas? What could she get out of it? Unless she's going to fuck with Cas, which, let's be real, Dean's done a better job of that.

He doesn't want to show signs that he's at all considering that she's not lying; he has a hard time believing that she really loves him like she's saying, but he'll bite that she, like, genuinely doesn't want to kill him or turn on him. That's as far as Dean can get on believing in "demon love."

"Why're you telling me, then?"