Why is Cupid associated with Valentine's Day?

Cupid (Greek: Eros) is associated with Valentines Day because he is the god of sexual love/desire. His parents were the God of War Mars (Greek: Ares) and the goddess of love Venus (Greek: Aphrodite). Because of his mother being goddess of love, and himself being the god of sexual desire, Cupid has become a big part of Valentines Day. The way he would get people to fall in love with each other was to shoot his special arrows at them.