Celia is Corvino's wife; she is also an important plot device. It is Volpone's desire that delivers her to his doorstep. Her presence there gives Bonario a chance to save her.
Bonario is the good fellow of the play; he is also sentimentally romantic. Celia and Bonario are foolish as well as innocent. They look at life in Venice through the eyes of lovers of melodramatic, romantic fiction. Therefore, they are not human beings who suffer through uncontrollable circumstances. Rather, they seriously misjudge the people they should know best because of their naive ideas about human nature.
If the gulls seem inhuman in their total greed, Bonario and Celia are equally inhuman in their purity. Their folly is more silly than vicious, but it is, nonetheless, folly.