In addition to the excellent remarks concerning Juliet's maturity above:

In Romeo and Juliet Act III, scene ii, Juliet has discovered from the Nurse that her cousin Tybalt is dead, and it was Romeo who killed him.  Juliet is visibly upset, and the Nurse thinks it's because she's mourning the death of Tybalt.  But, Juliet is more worried over Romeo's exile: will she ever see him again?

Here's a section of the monologue she says to the Nurse:

My husband lives, that Tybalt would have slain;
And Tybalt's dead, that would have slain my husband: All this is comfort; wherefore weep I then?

This is a kind of interior monologue, a mini-soliloquy, almost an aside.  Juliet is trying to rationalize the situation and calm herself down.  Her logical side is trying to talk some sense into her emotional side.  Her statement is a syllogism: "my husband is alive, and the man who tried to kill him is dead; therefore, I should be happy."  Although, it ends with a rhetorical question that she doesn't have an answer to.  Juliet would be happy, but the fact that Romeo is banished is a fate as bad as death.

Notice, the Nurse does not try to comfort her or help her plan any more rendezvous with Romeo after this.  The Nurse is completely emotional, and so Juliet must talk herself into action.  This scene thus ends their relationship.

In a similar scene at the Friar's, Romeo will be more emotional than Juliet.  He will try to kill himself, but Friar Lawrence will talk him out of it.  Friar Lawrence's advice to Romeo sounds almost identical to Juliet's words:

thy Juliet is alive,
For whose dear sake thou wast but lately dead;
There art thou happy: Tybalt would kill thee,
But thou slew'st Tybalt; there are thou happy too:

So after this, Juliet, betrayed by her family and the Nurse, will seek guidance from Friar Lawrence too.  By staging her suicide, Friar Lawrence will be their only intercessor in their post-exile reunion.

A couple things to remember:

1.  this is just after Tybalt kills Mercutio then is murdered by Romeo because of it.
2.  Juliet is related to Tybalt (and loves him).
3.  Juliet is married to Romeo.
3.  "Wherefore" = why, not where

Juliet is in emotional torment (internal conflict).  On one hand, she's relieved that Romeo did not die -as she expected Tybalt was out to kill him- ("why should I be crying?")  But she is freaking out that Romeo has murdered her cousin.  This could of course result in numerous consequences, none of which seem to have a happy ending.  She is truly grief stricken at the death of her cousin.  Keep that in mind.  But she is also madly (and somewhat childishly) in love with Romeo.  Don't forget she is also only 13.  This scene is actually a turning point in Juliet's maturity - as in, it grows a little.