Zeus is the Greek God of the sky, weather, air, justice, honor, humanity. He is also the King of the Gods. The youngest child of Kronos and Rhea, Zeus was saved from his father by his mother and raised in secret. He then returned to Mount Orthys--the Titan stronghold--to free his devoured siblings and waged war against their father. He currently leads the Olympian Council.
Zeus Overthrew his Father, Kronos, in his youth.
Hera is Zeus's sister and wife, and the Queen of Olympus. He fell deeply in love with her in their youth and spent centuries wooing her into agreeing to marry him. For decades afterward, the two were perfectly happy.
Unfortunately, Zeus is not one to happily remain with a single lover. Over the millennia, he had had thousands of affairs which had strained his relationship with Hera. She, as the Goddess of Marriage, wants monogamy from him--or, at least honesty. His refusal to even discuss the problem with her leads to wild bouts of rage and jealousy from the Queen.
Ganymede was a Trojan prince who Zeus fell deeply in love with. For over a year, he hid from Olympus, courting and wooing the young man. At the end of the year, Zeus brought his lover, whom he le loved as much as his own wife, to Olympus and granted him immortality. To protect him from Hera's rage, he also named Ganymede Cup-Bearer of the gods.
Unlike Hera, Ganymede recognizes that Zeus is not one to keep a single lover, and he does not wish to restrict the man he loves. As such, the two of them merely agree to be honest with each other about their affairs as to ensure that their relationship is open and honest.