So Menelao is this guy who falls in love with Elena (Helen) of Troy (who doesn't?) and takes the novel approach of dressing like a girl in order to get closer to her. (A lot of that sort of thing seems to happen in Cavalli operas.) I think by the time they get to this scene, Elena knows he's a guy, even though he's still wearing a dress. So they fall in love and sing this gorgeous duet.
