But soft, what light through yonder window breaks? It is the east, and Juliet is the sun. Arise, fair sun, and kill the envious moon, Who is already sick and pale with grief that thou her maid art far more fair than she. Be not her maid, since she is envious. Her vestal livery is but sick and green and none but fools do wear it. Cast it off.
Act 2, Scene 2
Holy Saint Francis, what a change is here! Is Rosaline, whom thou didst love so dear, So soon forsaken? Young men's love then lies Not truly in their hearts, but in their eyes.
Act 2, Scene 2
Three words, Romeo, and good night indeed. If that thy bent of love be honorable, thy purpose marriage, send me word tomorrow, by one that I’ll procure to come to thee, where and what time thou wilt perform the rite, and all my fortunes at thy foot I’ll lay and follow thee my lord throughout the world
After meeting Juliet for the first time, Romeo is professing his love for her. He's making drastic comparisons of Juliet to the sun and how she brings life to the world every morning, and how she is more beautiful and fairer than any other maiden in Verona.
Friar Lawrence is taken by surprise by Romeo's desire to marry Juliet. Romeo was courted with Rosaline for the longest time, and for him to just throw out that relationship for a maiden he just met is surprising.
Romeo and Juliet are already discussing marriage, after the second visit, because they know they are perfect for one another. Although, rushing love can end up going south very quickly.