What is the meaning of the phrase thou art wedded to calamity”?

Enter Friar Lawrence.

FRIAR LAWRENCE
Romeo, come forth; come forth, thou fearful man.
Affliction is enamored of thy parts,
And thou art wedded to calamity.

Enter Romeo.

ROMEO
Father, what news? What is the Prince’s doom?
What sorrow craves acquaintance at my hand 5
That I yet know not?

FRIAR LAWRENCE Too familiar
Is my dear son with such sour company.
I bring thee tidings of the Prince’s doom.

ROMEO
What less than doomsday is the Prince’s doom? 10

FRIAR LAWRENCE
A gentler judgment vanished from his lips:
Not body’s death, but body’s banishment.

Romeo is hiding out at Friar Lawrence's, and Friar updates him on the Tybalt situation.

ROMEO
Ha, banishment? Be merciful, say “death,”
For exile hath more terror in his look,
Much more than death. Do not say “banishment.” 15

FRIAR LAWRENCE
Here from Verona art thou banishèd.
Be patient, for the world is broad and wide.

ROMEO
There is no world without Verona walls
But purgatory, torture, hell itself.
Hence “banishèd” is “banished from the world,” 20
And world’s exile is death. Then “banishèd”
Is death mistermed. Calling death “banishèd,”
Thou cutt’st my head off with a golden ax
And smilest upon the stroke that murders me.

The Friar wants him to see the banishment as good news—yay for no executions?—but Romeo is too focused on the never seeing Juliet again part.

FRIAR LAWRENCE
O deadly sin, O rude unthankfulness! 25
Thy fault our law calls death, but the kind prince,
Taking thy part, hath rushed aside the law
And turned that black word “death” to
“banishment.”
This is dear mercy, and thou seest it not. 30

ROMEO
’Tis torture and not mercy. Heaven is here
Where Juliet lives, and every cat and dog
And little mouse, every unworthy thing,
Live here in heaven and may look on her,
But Romeo may not. More validity, 35
More honorable state, more courtship lives
In carrion flies than Romeo. They may seize
On the white wonder of dear Juliet’s hand
And steal immortal blessing from her lips,
Who even in pure and vestal modesty 40
Still blush, as thinking their own kisses sin;
But Romeo may not; he is banishèd.
Flies may do this, but I from this must fly.
They are free men, but I am banishèd.
And sayest thou yet that exile is not death? 45
Hadst thou no poison mixed, no sharp-ground
knife,
No sudden mean of death, though ne’er so mean,
But “banishèd” to kill me? “Banishèd”?
O friar, the damnèd use that word in hell. 50
Howling attends it. How hast thou the heart,
Being a divine, a ghostly confessor,
A sin absolver, and my friend professed,
To mangle me with that word “banishèd”?

FRIAR LAWRENCE
Thou fond mad man, hear me a little speak. 55

ROMEO
O, thou wilt speak again of banishment.

FRIAR LAWRENCE
I’ll give thee armor to keep off that word,
Adversity’s sweet milk, philosophy,
To comfort thee, though thou art banishèd.

ROMEO
Yet “banishèd”? Hang up philosophy. 60
Unless philosophy can make a Juliet,
Displant a town, reverse a prince’s doom,
It helps not, it prevails not. Talk no more.

FRIAR LAWRENCE
O, then I see that madmen have no ears.

ROMEO
How should they when that wise men have no eyes? 65

FRIAR LAWRENCE
Let me dispute with thee of thy estate.

ROMEO
Thou canst not speak of that thou dost not feel.
Wert thou as young as I, Juliet thy love,
An hour but married, Tybalt murderèd,
Doting like me, and like me banishèd, 70
Then mightst thou speak, then mightst thou tear thy
hair
And fall upon the ground as I do now,
Romeo throws himself down.
Taking the measure of an unmade grave.

The Friar tries every trick in the book to get Romeo to see banishment, instead of death, as a good thing. He tries to shame him for being ungrateful; he tells him life is long and the world is wide; he tries logic, philosophy, and even begging. Romeo's response? He throws himself down on the ground and says he wishes he was dead.  

Knock within.

FRIAR LAWRENCE
Arise. One knocks. Good Romeo, hide thyself. 75

ROMEO
Not I, unless the breath of heartsick groans,
Mistlike, enfold me from the search of eyes.

Knock.

FRIAR LAWRENCE
Hark, how they knock!—Who’s there?—Romeo,
arise.
Thou wilt be taken.—Stay awhile.—Stand up. 80

Knock.

Run to my study.—By and by.—God’s will,
What simpleness is this?—I come, I come.

Knock.

Who knocks so hard? Whence come you? What’s
your will?

There's a knock at the door. It may be the Prince's men. Eek. The Friar tells Romeo to hide, but Romeo refuses to move from his tantrum spot. 

NURSE, within
Let me come in, and you shall know my errand. 85
I come from Lady Juliet.

FRIAR LAWRENCE, admitting the Nurse
Welcome, then.

Enter Nurse.

NURSE
O holy friar, O, tell me, holy friar,
Where’s my lady’s lord? Where’s Romeo?

FRIAR LAWRENCE
There on the ground, with his own tears made 90
drunk.

Luckily for everyone, it's only the Nurse at the door. She asks where Romeo is and the Friar points him out. Yes, Romeo is still lying on the floor. 

NURSE
O, he is even in my mistress’ case,
Just in her case. O woeful sympathy!
Piteous predicament! Even so lies she,
Blubb’ring and weeping, weeping and blubb’ring.— 95
Stand up, stand up. Stand an you be a man.
For Juliet’s sake, for her sake, rise and stand.
Why should you fall into so deep an O?

ROMEO Nurse.

NURSE
Ah sir, ah sir, death’s the end of all. 100

ROMEO, rising up
Spakest thou of Juliet? How is it with her?
Doth not she think me an old murderer,
Now I have stained the childhood of our joy
With blood removed but little from her own?
Where is she? And how doth she? And what says 105
My concealed lady to our canceled love?

NURSE
O, she says nothing, sir, but weeps and weeps,
And now falls on her bed, and then starts up,
And “Tybalt” calls, and then on Romeo cries,
And then down falls again. 110

The Nurse observes Romeo and says he's just as bad off as Juliet, who keeps weeping and blubbering, calling out Romeo's name, then Tybalt's name, and then falling down and starting the process all over again. 

ROMEO As if that name,
Shot from the deadly level of a gun,
Did murder her, as that name’s cursèd hand
Murdered her kinsman.—O, tell me, friar, tell me,
In what vile part of this anatomy 115
Doth my name lodge? Tell me, that I may sack
The hateful mansion.

He draws his dagger.

Romeo, who's clearly losing it, decides that the best thing he can do is stab himself as punishment for hurting Juliet. 

FRIAR LAWRENCE Hold thy desperate hand!
Art thou a man? Thy form cries out thou art.
Thy tears are womanish; thy wild acts denote 120
The unreasonable fury of a beast.
Unseemly woman in a seeming man,
And ill-beseeming beast in seeming both!
Thou hast amazed me. By my holy order,
I thought thy disposition better tempered. 125
Hast thou slain Tybalt? Wilt thou slay thyself,
And slay thy lady that in thy life lives,
By doing damnèd hate upon thyself?
Why railest thou on thy birth, the heaven, and earth,
Since birth and heaven and earth all three do meet 130
In thee at once, which thou at once wouldst lose?
Fie, fie, thou shamest thy shape, thy love, thy wit,
Which, like a usurer, abound’st in all
And usest none in that true use indeed
Which should bedeck thy shape, thy love, thy wit. 135
Thy noble shape is but a form of wax,
Digressing from the valor of a man;
Thy dear love sworn but hollow perjury,
Killing that love which thou hast vowed to cherish;
Thy wit, that ornament to shape and love, 140
Misshapen in the conduct of them both,
Like powder in a skilless soldier’s flask,
Is set afire by thine own ignorance,
And thou dismembered with thine own defense.
What, rouse thee, man! Thy Juliet is alive, 145
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.
The law that threatened death becomes thy friend
And turns it to exile: there art thou happy. 150
A pack of blessings light 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. 155
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 time 160
To blaze your marriage, reconcile your friends,
Beg pardon of the Prince, and call thee back
With twenty hundred thousand times more joy
Than thou went’st forth in lamentation.—
Go before, nurse. Commend me to thy lady, 165
And bid her hasten all the house to bed,
Which heavy sorrow makes them apt unto.
Romeo is coming.

The Friar gives Romeo a pep talk, telling him all the things he should be thankful for. Juliet is alive, he wasn't killed by Tybalt, and he hasn't been executed for killing Tybalt. Romeo should count his blessings here, not obsess over that one word, "banished." Next the Friar offers a better plan that doesn't involve Romeo stabbing himself. He says Romeo and Juliet can have one night together before Romeo leaves Verona. After that, Romeo has to go, but the Friar also promises that they'll find a way to get Romeo pardoned by the Prince so he can come back to Verona and make his marriage to Juliet public knowledge.

NURSE
O Lord, I could have stayed here all the night
To hear good counsel. O, what learning is!— 170
My lord, I’ll tell my lady you will come.

ROMEO
Do so, and bid my sweet prepare to chide.

NURSE
Here, sir, a ring she bid me give you, sir.
Nurse gives Romeo a ring.
Hie you, make haste, for it grows very late.
She exits.

ROMEO
How well my comfort is revived by this! 175

FRIAR LAWRENCE
Go hence, good night—and here stands all your
state:
Either be gone before the watch be set
Or by the break of day disguised from hence.
Sojourn in Mantua. I’ll find out your man, 180
And he shall signify from time to time
Every good hap to you that chances here.
Give me thy hand. ’Tis late. Farewell. Good night.

ROMEO
But that a joy past joy calls out on me,
It were a grief so brief to part with thee. 185
Farewell.

They exit.

The Nurse and Romeo are both thrilled and greatly relieved by the Friar's words, and everyone parts with happy farewells. 

Brain Snack: Marriages in the Catholic Church (and lots of other churches) aren't considered valid unless they'd been consummated—i.e., the two people have to have sex. If Juliet and Romeo don't sleep together, Juliet's dad will be able to get the marriage declared invalid and marry her off to Paris.