During the course of the play, Romeo matures from adolescence to adulthood as a result of his love for Juliet and his unfortunate involvement in the feud, marking his development from a comic character to a tragic figure.
Romeo is initially presented as a Petrarchan lover, a man whose feelings of love aren't reciprocated by the lady he admires and who uses the poetic language of sonnets to express his emotions about his situation. Romeo's exaggerated language in his early speeches characterizes him as a young and inexperienced lover who is more in love with the concept of being in love than with the woman herself.
The play's emphasis on characters' eyes and the act of looking accords with Romeo's role as a blind lover who doesn't believe that there could be another lady more fair than his Rosaline. Romeo denies that he could be deluded by love, the "religion" of his eye. This zeal, combined with his rejection of Benvolio's advice to find another love to replace Rosaline, highlights Romeo's immaturity as a lover. Similar imagery creates a comic effect when Romeo falls in love at first sight with Juliet at the Capulet feast. When Romeo sees Juliet, he realizes the artificiality of his love for Rosaline: "Did my heart love till now? Forswear it, sight! / For I ne'er saw true beauty till this night" (I.5.52-53).
As the play progresses, Romeo's increasing maturity as a lover is marked by the change in his language. He begins to speak in blank verse as well as rhyme, which allows his language to sound less artificial and more like everyday language.
The fated destinies of Romeo and Juliet are foreshadowed throughout the play. Romeo's sense of foreboding as he makes his way to the Capulet feast anticipates his first meeting with Juliet:
my mind misgives
Some consequence yet hanging in the stars
Shall bitterly begin his fearful date
Romeo's role first as a melancholy lover in the opening scenes of the play and then as a Juliet's secret love is significant. Romeo belongs in a world defined by love rather than a world fractured by feud. Tybalt's death in Act III, Scene 1, brings about the clash between the private world of the lovers and the public world of the feud. Romeo is reluctant to fight Tybalt because they are now related through Romeo's marriage to Juliet.
When Tybalt kills Mercutio, however, Romeo (out of loyalty to his friend and anger at Tybalt's arrogance) kills Tybalt, thus avenging his friend's death. In one ill-fated moment, he placed his love of Juliet over his concern for Mercutio, and Mercutio was killed. Romeo then compounds the problem by placing his own feelings of anger over any concerns for Juliet by killing Tybalt.
Romeo's immaturity is again manifest later when he learns of his banishment. He lies on the floor of the Friar's cell, wailing and crying over his fate. When the Nurse arrives, he clumsily attempts suicide. The Friar reminds him to consider Juliet and chides him for not thinking through the consequences of his actions for his wife.
The Friar then offers a course of action to follow, and Romeo becomes calm. Later, when Romeo receives the news of Juliet's death, he exhibits maturity and composure as he resolves to die. His only desire is to be with Juliet: "Well Juliet, I will lie with thee tonight" (V.1.36). His resolution is reflected in the violent image he uses to order Balthasar, his servant, to keep out of the tomb:
The time and my intents are savage-wild,
More fierce and more inexorable far
Than empty tigers or the roaring sea.
After killing Paris, Romeo remorsefully takes pity on him and fulfills Paris' dying wish to be laid next to Juliet. Romeo notes that both he and Paris are victims of fate and describes Paris as: "One writ with me in sour misfortune's book" (V.3.83) since Paris experienced an unreciprocated love from Juliet similar to Romeo's unrequited love for Rosaline. Romeo is also filled with compassion because he knows that Paris has died without understanding the true love that he and Juliet shared.
Romeo's final speech recalls the Prologue in which the "star-cross'd" lives of the lovers are sacrificed to end the feud:
Will I set up my everlasting rest
And shake the yoke of inauspicious stars
From this world wearied flesh.