Marriage was a monogamous institution in the Greco-Roman world. A primary purpose of marriage was to produce legitimate children, and the attraction that Eros, also known as Cupid or Amor to the Romans, could bring to the marriage union certainly helped to achieve that end. The god's appearance in marriage scenes such as this one was common.
McCann, Anna Marguerite. 1978. Roman Sarcophagi in the Metropoltian Museum of Art. no. 21, pp. 124-29, 1, fig. 157, New York: The Metropolitan Museum of Art.
Kleiner, Diana and Susan B. Matheson. 1996. I Claudia: Women in Ancient Rome p. 208, fig. 163, New Haven: Yale University Art Gallery.