Venus is the Roman goddess of love and sexuality, and is similar to the Greek Aphrodite. She is the mother of Cupid and wife to the god Vulcan. She is said to have been born of the foam that sprayed from the ocean after castrated genitals of Cronos/Uranus were flung in. (There is some disagreement as to whether it was Jupiter or Gaea who castrated Cronos.)
Venus was believed to be the mother of the Aeneas, the Trojan warrior who lead survivors to the site of what would become Rome. Julius Cesar claimed to be a descendant of Venus through Aeneas' line and began the cult of Venus Genetrix (Mother Venus).
Much of the mythology surrounding Venus has to do with the sexual (mis)adventures. One of the best known deals with Her desire for a mortal. Cupid had accidentally wounded Venus with one of his arrows and found Herself captivated by Adonis. She left Olympus to be with him, neglecting Her duties. One day She was called away from him, and before leaving warned him to be aware of wild animals. But before She could arrive at Her destination, She heard his cries of pain--Adonis had been gored by a boar and lay dying. In Her grief, She changed the blood of Adonis into the beautiful anemone flower.
Traditionally, the Lovers card deals with choice, often involving decisions about love and romance. With Venus, this card points very strongly towards sexual relationships. She is a joyous goddess, so these are likely to be happy encounters. However, caution must be exercised, as Venus did have more then Her fair share of romantic problems.
Reversed, this card represents infidelity or unstable emotions. It warns of the need for abstinence until the relationship is better defined. It can also point to unhealthy possessiveness within a relationship.