Judging from the look on her face, she knows exactly how you're react and isn't the slightest bit worried you'll flip out (you know, like a normal husband would.) She knows that you'll take in the scene and whisper, so as not to alert the guy to your presence, "now or later?"
Now or later?
As in, does she want you to lick his cum out of her pussy now, before he leaves, or later, after he's gone.
"Now," she says, "he'll want to watch."