You have here a fine example of the course of action of Little Death.
A few moments ago, Li’l D announced his imminent action to Big D, which in the common sense would imply some sort of sexual arousement (and yes, there ARE readers who actually expected Death to get laid after going up to the girl’s place!).
But no. In this case, it meant the shock that befell poor Death when he learned that Mercedes had a boyfriend. Just take a look at the poor guy’s eyes and you’ll see what I mean.
As I said: A Little Death can also stand for a sudden negative experience.