How does Romeo deal with his banishment in act 3?

The always emotional Romeo is hiding out in Friar Laurence's cell when he finds out he has been banished from Verona for killing Tybalt. Rather than experiencing gratitude that he has been spared the death penalty, he reacts very badly, feeling his life is over because he will be separated from his beloved Juliet. All the woes of the world seem to have to have fallen on his head. The friar scolds him and admonishes him to get a grip.
Juliet's nurse shows up with tokens of esteem from Juliet, but Romeo—perhaps not surprisingly, given he has just killed her cousin—fears she is angry at him. He threatens to stab himself and end it all. The friar tells him if he does, then his love for Juliet is a lie—"perjury"—for his death would kill Juliet, the beloved he had "vowed to cherish." Romeo's "wit," or intelligence, would be warped ("misshapen") if he acted so rashly:

Thy dear love sworn but hollow perjury,
Killing that love which thou hast vowed to cherish;
Thy wit, that ornament to shape and love,
Misshapen in the conduct of them both
Romeo sees reason and listens to the friar's counsel, but his impulsive and emotional behavior foreshadows how he will react when he thinks Juliet is dead near the end of the play.