What song represents each character in Romeo and Juliet?
I'm not sure what your question is referring to so I will offer a couple of alternatives. If you're asking about modern songs that could be applied to Shakespeare's Romeo and Juliet I've provided a couple of links below that may be helpful.
You might also be referring to the beginning of Act III, Scene 5. It is the morning after the two have consummated their marriage and Juliet does not want the night to end. She says she hears a nightingale singing outside her window. The bird, of course, is the symbol of the night. She tells Romeo,
Wilt thou be gone? It is not yet near day.
It was the nightingale, and not the lark,
That pierced the fearful hollow of thine ear.
Nightly she sings on yond pomegranate tree.
Believe me, love, it was the nightingale.
More light and light, more dark and dark our woes.
It was the lark, the herald of the morn,
No nightingale. Look, love, what envious streaks
Do lace the severing clouds in yonder east.
Night’s candles are burnt out, and jocund day
Stands tiptoe on the misty mountain-tops.
I must be gone and live, or stay and die.