While young Romeo is very impulsive and follows his "violent delights" without heeding the advice of wiser adults such as Friar Lawrence, who warns against the "violent ends" of these delights, Romeo does gradually begin to consider the consequences of his actions.
In Act III, for instance, recklessly injects himself into the altercation between Mercutio and Tybalt. He tells Tybalt that now he loves him, a statement which has caused Mercutio to draw his sword in his anger at Romeo's "vile submission." Tybalt then stabs Mercutio under Romeo's arm, and Romeo in turn slays Tybalt.
Romeo's impulsive actions have wrought tragedy, and he regrets them. Later in Act V, a more mature Romeo apologizes to Tybalt in the tomb of the Capulets:
Oh, what better favor can I do for you than to kill the man who killed you with the same hand that made you die young. Forgive me, cousin! (5.3.104-106)
Later as Romeo encounters Paris at the tomb, he demonstrates maturity because he does not want to fight. He begs Paris to leave him alone:
Put not another sin upon my headBy urging me to fury. O, be gone!By heaven, I love thee better than myself,For I come hither armed against myself.Stay not, be gone. Live, and hereafter sayA madman’s mercy bid thee run away. (5.3.70-75)
As a character, Romeo matures throughout the play in terms of finally accepting responsibility for his own actions.
Throughout the play, Romeo makes many rash decisions that lead to deadly consequences. Moments after killing Tybalt in Act III, Scene 1, Romeo shows his immaturity by blaming Juliet, who wasn't even there, for killing Tybalt. On page 46, he says,
O sweet Juliet,
Thy beauty hath made me effeminate,
And in my temper soften'd valour's steel!
In other words, Romeo claims Juliet's beauty turned him more feminine and caused him to react on his feelings instead of use his head. By the end of the play, though, Romeo not only apologizes to Tybalt for taking his life, but also recognizes him as his own family. On page 86, Romeo says,
Tybalt, liest thou there in thy bloody sheet?
O, what more favour can I do to thee
Than with that hand that cut thy youth in twain
To sunder his that was thine enemy?
Forgive me, cousin!
Romeo accepts responsibility for killing Tybalt by referring to "that hand"—his own. He asks Tybalt for forgiveness and refers to him as his cousin. Romeo refers to Tybalt as his family because of his marriage to Juliet, and it also shows Romeo is burying the feud and accepting his role as part of the problem.
***Please note that the page numbers correspond to the Dover Thrift Editions of Romeo and Juliet.***