This is the moment when Juliet is forced to act on her own. Up until this point, she has made every attempt to be an obedient daughter. She has trusted the Nurse to guide her in any situation. However, faced with her betrayal, Juliet rejects both her parents and the Nurse, seeking advice from the Friar. She has matured beyond blind submission, rejected the offer of marriage from Paris, and is now willing to leave her home behind for Romeo. Having essentially been kicked out of her home by her father, and abandoned by her nurse, Juliet is now taking control of her own life.
The answers to your questions can be found in the following passage from Act 3 Scene 5
Faith, here it is.
Romeo is banish'd; and all the world to nothing,
That he dares ne'er come back to challenge you;
Or, if he do, it needs must be by stealth.
Then, since the case so stands as now it doth,
I think it best you married with the county.
O, he's a lovely gentleman!
Romeo's a dishclout to him: an eagle, madam,
Hath not so green, so quick, so fair an eye
As Paris hath. Beshrew my very heart,
I think you are happy in this second match,
For it excels your first: or if it did not,
Your first is dead; or 'twere as good he were,
As living here and you no use of him.
Speakest thou from thy heart?
And from my soul too;
Or else beshrew them both.
Well, thou hast comforted me marvellous much.
Go in: and tell my lady I am gone,
Having displeased my father, to Laurence' cell,
To make confession and to be absolved.
Marry, I will; and this is wisely done.
Ancient damnation! O most wicked fiend!
Is it more sin to wish me thus forsworn,
Or to dispraise my lord with that same tongue
Which she hath praised him with above compare
So many thousand times? Go, counsellor;
Thou and my bosom henceforth shall be twain.
I'll to the friar, to know his remedy:
If all else fail, myself have power to die.
Juliet has just been ordered by her father to marry a man other than Romeo. Juliet protests, provoking her father's fury. Nurse defends Juliet from her father, but then advises Juliet to forget about Romeo, for he is "banish'd" and accept Paris is a "lovely gentleman." Nurse compares Romeo and Paris, declaring that Romeo's a "dishclout" to Paris.
Juliet states "Amen!" and pretends to accept Nurse's advice. Thanking her nurse for comforting her "marvellous much," Juliet is in fact tricking her nurse into thinking that she has accepted her betrothal to Paris, when in fact, on the inside, she is cursing Nurse for insulting Romeo. Cutting all ties with Nurse, Juliet seeks Friar Lawrence for a way to resolve her plight.