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
Act 2 Scene 3
Virtue itself turns vice, being misapplied, And vice sometime by action dignified
Act 2 Scene 4
An he speak anything against me, I’ll take him down
Juliet is fresh and new like a sunrise, whereas Rosaline - like the moon - fades away when the sun comes up. Although Juliet does not know about Rosaline, the play suggests that Juliet is jealous of Rosaline because the sun is killing the moon. Juliet is not killing Rosline, but rather pushing her away.
Friar Lawrence talks about how the love story between Romeo and Juliet is like a rose - sweet but has many thorns or obstacles - in act one. In act 2 we see him talking about how love can be beautiful but only if the actions you take part in are ethical. He talks about how love can take revenge on you and it may lead to an unsettling fate.
The Nurse is talking to Romeo about Mercutio's behavior. The Nurse tells Romeo that if him and his friends are rude to her, then he is not a match for Juliet and he should find someone else. The Nurse tells Romeo that if she even hears of him speaking of another women like that again, she will not let him marry Juliet and she will make his life terrible.