:: Discreetly spit it out into a tissue.
[[You]] don't want to swallow it, but you also don't want to offend him so you pull your head off when you're sure he's done and discreetly grab a tissue.  You turn your head and spit his semen into the tissue, crumpling it up and hiding it in your hand.  You turn back to Billy and smile at him.

<<display "Goodnight to Billy">>