Why does Friar Laurence criticize Romeo for his suicide attempt? What reasons does the Friar give Romeo for living? What reasons may Friar Laurence have for his own feelings?

In act 3, scene 3 of Romeo and Juliet, Friar Laurence tells Romeo that, as punishment for killing Tybalt, the Prince has banished him from Verona. Romeo laments that this sentence is worse than execution. He would rather be dead than be separated from Juliet.
Friar Laurence calls Romeo ungrateful; according to the laws, Romeo should be put to death, but the Prince was kind and changed the sentence to banishment. Romeo still believes death would be kinder than banishment from Juliet, and he literally falls on the ground. The Nurse arrives, and Friar Laurence says Romeo is:

There on the ground with his own tears made drunk.

Friar Laurence and the Nurse criticize Romeo for his behavior. Still, Romeo draws his sword, as if to hurt himself:

ROMEO: As if that name,Shot from the deadly level of a gun,Did murder her, as that name's cursed handMurdered her kinsman. O tell me, friar, tell me,In what vile part of this anatomyDoth my name lodge? Tell me, that I may sackThe hateful mansion.
[Drawing his sword.]
FRIAR:Hold thy desperate hand.Art thou a man? Thy form cries out thou art.Thy tears are womanish; thy wild acts denoteThe unreasonable fury of a beast.

The Friar tells Romeo to think of all the things he should be grateful for: Juliet is alive, Tybalt could have killed Romeo but Romeo is alive, the Prince could have executed Romeo but he was only banished:

What, rouse thee, man! Thy Juliet is alive,For whose dear sake thou wast but lately dead:There art thou happy. Tybalt would kill thee,But thou slewest Tybalt: there art thou happy too.The law that threatened death becomes thy friendAnd turns it to exile: there art thou happy.A pack of blessings lights up upon thy back, Happiness courts thee in her best array;But, like a misbehaved and sullen wench,Thou pouts upon thy fortune and thy love.Take heed, take heed, for such die miserable.Go, get thee to thy love as was decreed,Ascend her chamber, hence and comfort her.But look thou stay not till the watch be set,For then thou canst not pass to Mantua,Where thou shalt live, till we can find a timeTo blaze your marriage, reconcile your friends, Beg pardon of the prince, and call thee backWith twenty hundred thousand times more joyThan thou wentest forth in lamentation.

Friar Laurence gives Romeo hope for the future by saying that Romeo can stay in Mantua until they can find a way to reunite him and Juliet and hopefully find a way to end his sentence of banishment.