In this monologue, the Nurse is telling Juliet to treat exiled Romeo as if he is dead. This has a devastating effect on Juliet, for obvious reasons. To connect this passage to your thesis, however, we must be a little more creative.
For your three arguments, you should break down what you mean when you say "everyone involved." This is most easily done by considering the Montagues, the Capulets, and Romeo and Juliet themselves.
First point: "Romeo is banish'd." Why is Romeo banished? Romeo killed Tybalt, a Capulet. Explain why this is a tragedy for the Capulet family, and talk of the circumstances surrounding the death.
Second point: "If he do [come back], it needs must be by stealth." What is the effect of Romeo's banishment on his family? Here you can go into detail about the suffering of the Montague family. These first two paragraphs thinly relate to the above passage, because the nurse is addressing Juliet's specific question of what she must do about Romeo's exile. To build a more solid argument, you must either change the thesis or choose a different passage.
Third point: "Or if it did not, your first is dead." Here the Nurse tells Juliet that even if Paris is not as good a suitor as Romeo, Romeo's exile essentially means that he is dead. Juliet's response at the end of the scene indicates that she would rather kill herself than live without Romeo. "If all else fail, myself have power to die." It is easy to explain the strong negative effect on Juliet and to speculate the same for Romeo.