Tom and Daisy Buchanan are husband and wife. They have been married for a few years, have a daughter named Pamela, and are incredibly rich. Tom inherited his fortune. He also has frequent extramarital affairs, of which Daisy is aware. In fact, the day before her wedding, she got very drunk and told her friend, Jordan, that she didn't want to marry Tom. She doesn't seem to love him anymore, though he claims to love her still.
Tom's most recent affair is with Myrtle Wilson. She is married to George Wilson, the owner of a garage and gas station in the valley of ashes, but Myrtle considers George beneath her. She aspires to become Tom's wife, failing to realize he never considers her his equal; he strikes her in the face just for speaking his wife, Daisy's, name. Myrtle enjoys the status that being Tom's mistress seems to confer upon her among the people who are aware of their dalliance.
After years of Tom cheating on her, when Daisy is reunited with Gatsby, she seems to have no qualms about having an affair with him, her former lover. She and Gatsby were lovers before she married Tom. When Gatsby was shipped off to war, Daisy found she could not wait for him to return; she needed her life to be settled now, so she settled on Tom. Since then, Gatsby has made a fortune as a bootlegger, and he purchased a mansion across the bay from Daisy's home. Once Daisy finds out the illegal way Gatsby made his fortune, she abandons him and returns to her husband, but still allows Gatsby to take the blame for Myrtle Wilson's death. She doesn't even send a flower to his funeral, which is made even worse when considering she is also indirectly responsible for his death.