The next time you're fucking her, wait until you're right about to cum. When she goes all "babe, get the towel" on you, hold her down by the throat and stare her straight in the eyes while you cum all over her pussy and chest. Don't fucking injure the girl, but don't be a pussy about it either.
What you do from there is all you. Be a man about it, or bring up the pic, or a combo of both.
