Analyzing a literary device in Catullus 2

Catullus uses a sparrow in this poem as a symbol for his ideal relationship with his wife. He describes the bird as bringing joy and relieving his wife of a depression which she faces. Catullus is saddened that he cannot bring the same joy to Lesbia as the bird does. (“how I wish I could sport with you as she does, /bring some relief to the spirit’s black depression!”) The reason for this depression can be the do the unhealthy relationship Catullus has with Lesbia. The sparrow provides what he cannot.