Answer:
Romeo's lines make up one quatrain, which uses an abab rhyme scheme.
A quatrain is a four line stanza. Both Romeo and Juliet's lines are quatrains. Romeo's lines are the beginning of a sonnet and the rhyme scheme is abab. Juliet's lines switch to cdcd because of the sonnet form. A couplet are two rhyming lines one after another. A sonnet is 14 lines with 3 quatrains and one final rhyming couplet.