Gaston's fiance is cheating on him. He goes to a hotel with his uncle and finds her with another man kissing.
Aunt Alicia is shown taking bath. Only bare shoulders are visible.
Sex without marriage is implied often in the movie and being a courtesan rather than a wife is presented as a viable way of living. Near the beginning, one character says, "Where most women get married at once, we get married at last". But no sex or nudity is ever shown.
Gigi mentions "sharing your bed" when talking to Gaston. Then mentions "another man's bed" when he tires of her.