As has been noted, Romeo becomes emotional because of his unrequited love, Rosaline, he reacts to this in a childish way. He creates himself an artificial night, locking fair daylight out. (I.I) His parents are worried for him, and Benvolio promises Romeo that he will find him another girl. “If day
is life as Friar Lawrence says it is, then life is for Romeo and the enemy of love, which can exist in its purity only by itself, in the little death of a private darkness” Doren, Mark. Shakespeare. New York: H. Holt, 1939.
As a matter of fact, Benvolio and Mercutio persuade Romeo to go crash the Capulet’s party them to compare Rosaline to other beautiful women in Verona. Romeo reluctantly agrees and falls in love with Capulet’s daughter, Juliet, at first sight. The love is not unrequited, and soon Rosaline is forgotten. Soon after, they meet on the balcony and plan to marry. Romeo is standing in shadows of darkness, while comparing Juliet to the sun. He asks the sun to rise and kill the envious moon. He often compared Rosaline to the moon, and now his love for Juliet has outshone her. When Romeo steps out of the shadows, into the light from Juliet’s balcony, it is an example of his maturation for love. “As well as being a metaphor for death, night also distinguishes the private, personal world of the lovers from the public world of reason, law, and social responsibility, which Shakespeare associates here, and in a number of other plays as well, with the light of day. The characters of Romeo and Juliet who support the values of the public world prefer day to night.” Rackin, Phyllis. Shakespeare’s Tragedies. New York: Ungar, 1978.
All things considered, Mercutio's death, which played a crucial role in the play, changes the whole play into a tragedy. Mercutio was Romeo’s friend, who was known as a jokester. Before the death of Mercutio, Romeo and Juliet would have been considered a comedy, but after the death everything changed to a dark side. If Tybalt did not kill Mercutio, Romeo would not have looked for revenge and killed Tybalt, resulting in him being exiled from Verona.
Overall, Romeo and Juliet’s love was associated with night, not only physically, but emotionally and mentally as well. If Benvolio did not convince Romeo to go to the Capulet’s party, Romeo would still be in his little death of a private darkness. If Romeo did not step out of the shadows, into the light from Juliet’s balcony, he would have never matured, and if Mercutio never died, the play could have easily been confused with a comedy.