In Shakespeare's Romeo and Juliet, Romeo is first portrayed as a love-struck adolescent. In a conversation with Benvolio, Romeo complains that time is passing too slowly.
Ay me, sad hours seem so long.
Benvolio asks why Romeo's day moves so slowly...is it sadness? Romeo responds:
Not having that which, having, makes them short.
Intuitively, Benvolio asks if it has something to do with love; Romeo says:
Out of her favor where I am in love... (paraphrase and quotes of lines 157-164)
This conversation relates to his infatuation with Rosalind who does not return his love, wanting to join a convent instead. All Romeo is capable of at this point in the story is to sigh over Rosalind's rejection.
It would seem that by Act One, scene five, Romeo is changeable. When first he sees Juliet, thoughts of Rosalind are gone:
Oh, she doth teach the torches to burn bright...For I ne'er say true beauty till this night. (lines 42 and 51)
Romeo can also be said to fall in love quickly. When Romeo climbs the orchard walls to seek out Juliet, she is speaking alone—to the night, about him. When he reveals himself and makes himself known to her, she asks how he arrived: the walls are high, and he would be killed if caught, since he is a Montague on Capulet land. His explanation, however, speaks of "love;" though they have only just met that night, Romeo speaks to Juliet of love:
With love's light wings did I o'erperch these walls. (II.ii.65)
Romeo could be said to be impetuous: within hours of meeting her, he has proposed to Juliet, and very soon he and Juliet will marry, with the help of Friar Lawrence. Romeo meets Friar Lawrence to ask the holy friar to marry them:
Then plainly know my heart's dear love is set
On the fair daughter of rich Capulet;
As mine on hers, so hers is set on mine,
And all combin'd, save what thou must combine
By holy marriage. When, and where, and how
We met, we woo'd, and made exchange of vow,
I'll tell thee as we pass; but this I pray,
That thou consent to marry us to-day. (II.iii.59-66)
Romeo and Juliet have both pledged themselves in love and wish to marry that same day. Romeo tells the friar he will explain how this all has happened as they walk and talk, but he wants to marry immediately.
Finally, Romeo is an honorable man, true to his love of Juliet, though it costs him dearly. Once he is married, he refuses to fight with Tybalt because (unknown to the fiery-tempered Tybalt) Romeo is now a part of the family—being married to Juliet. He can't explain why, but Romeo only wants peace between them (though he has never really been involved in the feud as far as the audience can tell), but Tybalt is in deadly earnest of killing Montagues. Romeo addresses Tybalt:
I do protest I never injur'd thee,
But love thee better than thou canst devise
Till thou shalt know the reason of my love;
And so good Capulet, which name I tender
As dearly as mine own, be satisfied. (III.i.64-68)
(Of course, this is when Tybalt reaches beyond Romeo, killing Mercutio, who is also related to Prince Escalus. Romeo avenges the killing, and is banished from Verona, wherein the tragedy moves along quickly, and the young lovers both end up dead.)