Romeo speaks primarily in heroic couplets throughout the play. A heroic couplet is a rhyming pair of iambic pentameter lines. Iambic pentameter is a poetic line of iambs five metrical feet long. Oh...and an iamb is a foot of poetry that sounds like a heartbeat, just as the words "a-LONE" and "re-LEASE."
In other words, iambic pentameter has a beat that goes:
ba-DUM ba-DUM ba-DUM ba-DUM ba-DUM.
Here are some samples from Romeo's lips:
For beauty starved with her severity
Cuts beauty off from all posterity.
She is too fair, too wise, wisely too fair,
To merit bliss by making me despair:
She hath forsworn to love, and in that vow
Do I live dead that live to tell it now.
Prior to this, he even rhymes with a line of Benvolio's (and does this from time to time with others throughout the play). Benvolio says, "Then she hath sworn that she will still live chaste?" and Romeo responds: "She hath, and in that sparing makes huge waste...."