Quote 1
ROMEO
Love is a smoke raised with the fume of sighs;
Being purged, a fire sparkling in lovers' eyes;
Being vexed a sea nourish'd with loving tears:
What is it else? a madness most discreet,
A choking gall, and a preserving sweet.
(1.1.197-201)
These are pretty big words coming from a teenager. All this abstract language—love as "smoke," as "fire," as a "sea," as "madness"—suggest that maybe Romeo knows more about love from books than, you know, actually being in love.
Quote 2
ROMEO
Well, in that hit you miss. She'll not be hit
With Cupid's arrow. She hath Dian's wit,
And, in strong proof of chastity well armed,
From love's weak childish bow she lives unharmed.
She will not stay the siege of loving terms,
Nor bide th' encounter of assailing eyes,
Nor ope her lap to saint-seducing gold.
[…]
BENVOLIO
Then she hath sworn that she will still live chaste?
(1.1.216-222; 225)
Romeo admits that Rosaline has vowed to remain "chaste" like "Diana," the goddess of virginity and hunting. In other words, Rosaline has sworn off boys and sex, which means that Romeo has no chance of winning her heart. What's interesting about this passage is that Romeo sounds a whole lot like a typical "Petrarchan lover." Petrarch, by the way, was a fourteenth-century Italian poet whose sonnets were all the rage in Renaissance England. In fact, Shakespeare's own collection of Sonnets are, in part, inspired by Petrarch's love poetry, which was written about "Laura," a figure who was as unavailable and unattainable as Romeo's current crush (Rosaline). Petrarchan poetry happens to contain a lot of metaphors that equate the pursuit of love with hunting and/or battle. In this passage, Romeo says that Rosaline is well "arm'd" against the "siege" of his love and "Cupid's arrow," which is an elaborate way to say that Rosaline is physically and emotionally impenetrable.
Quote 3
ROMEO
When the devout religion of mine eye
Maintains such falsehood, then turn tears to fire;
And these who, often drowned, could never die,
Transparent heretics, be burnt for liars.
One fairer than my love? The all-seeing sun
Ne'er saw her match since first the world begun.
(1.2.95-100)
Romeo uses religious language to talk about Rosaline