Venus married Vulcan as part of a deal brokered by Jupiter. Vulcan, in exchange for freeing his mother, Juno (or Hera in Greek mythology), who he had trapped, demanded Venus's hand in marriage from Jupiter.
The Deal and the Marriage
Vulcan (Hephaestus in Greek mythology), the god of fire and the forge, was known for his skill in crafting. He used this skill to create a trap for his mother, Juno. Jupiter (Zeus), seeking to free his wife, was forced to negotiate with Vulcan. Vulcan, perhaps feeling slighted by the Olympians or simply desiring Venus, used his leverage to secure her as his bride.
A Loveless Union
The marriage between Venus and Vulcan was far from happy. Venus, the goddess of love and beauty, was known for her affairs, most notably with Mars (Ares), the god of war. Vulcan, being lame and considered unattractive by some, struggled to hold Venus's affection. Their relationship is often depicted as fraught with infidelity and unhappiness.
Summary
Venus's marriage to Vulcan was not based on love but rather on a bargain struck between Vulcan and Jupiter. Vulcan freed Juno in exchange for Venus's hand, resulting in a marriage characterized by Venus's infidelity and general unhappiness.
