Aidan looks at the hand first, like it might just be a man-eating plant in disguise, or maybe just like he doesn't know what to do with it (he wouldn't be sure what to do with a man-eating plant in disguise either, though, so the two aren't mutually exclusive).
Then he looks up at Nathaniel and he seems to like what he sees, because he purses his lips with an appreciative smile, nods his head, and shakes the fella's hand. "'Til next time." He turns, a hand in his pocket, the other waving goodbye to Nathaniel and the others, held high above his head and without a backward glance at them? Especially not at the singer who reminds him so much of her.
And maybe he'll buy Nathaniel a drink next time, who knows. Ah, probably not. He does enjoy his solitude. He's whistling on his way up and out, and he does a few jazz moves in the street. Tomorrow he might be dead; might as well enjoy himself while he could.