In Act 3, Scene iii, why does the Nurse look for Romeo after the fight? Where does she find him?
Remember that Romeo and Juliet were only married that day, and have yet to have their wedding night together. So the reason Romeo and Juliet need to see each other, beyond to be together in the time of tragedy, is to consummate their marriage. And that's basically what the Nurse says in Act 3, Scene 2:
Hie to your chamber. I'll find Romeo
To comfort you. I wot well where he is.
Hark ye, your Romeo will be here at night.
I'll to him; he is hid at Laurence’ cell.
O, find him! give this ring to my true knight
And bid him come to take his last farewell.
So she knows, even here, that he is hiding at Friar Laurence's cell. How does the nurse know where he is? Gossip, maybe someone has told her, or maybe she knows how close the Friar and Romeo are - the play doesn't really provide the answer. But in Act 3, Scene 3, she turns up at Friar Laurence's knowing, apparently, exactly where Romeo will be:
Let me come in, and you shall know my errand;
I come from Lady Juliet.
O holy friar, O, tell me, holy friar,
Where is my lady's lord, where's Romeo?