shakespeare creates tension
How does Shakespeare build tension in act 1 scene 5?

This is the end of act one. All the major elements are in place. The hatred of the Montagues and Capulets. That Romeo is lovesick and in love with the idea of love. The fate of what will befall the next person to disturb the peace. And now Romeo and Juliet in love. The curtain closes on a note of high drama and feeling. The storyteller has brought the audience to this height of feeling by potently and directly putting into play the elements of the story. Very little is withheld for some far off plot effect or revelation. What's important to setting up and advancing this story has been presented in a clear, dramatic way with poetic grace and wit.
In a script written by a struggling storyteller, one could imagine the brawl that opens Romeo and Juliet being the climax of act one. Because Shakespeare had a clear sense of his story and how to escalate its drama, he doesn't delay setting out the conflict that fuels it. In this story, if Shakespeare writes that one character doesn't like another, one can surmise they will meet in either that scene or the next. Because of this arrangement of the story's elements, the play's audience develops a sense of trust the author won't introduce characters for no clear dramatic purpose, introduce information but delay its import.
When Romeo is introduced, he is already lovesick, and very poetic and direct about it. What he's feeling isn't withheld to create a revelation at the end of act one. Because it defines Romeo, it comes out in his opening scene. Further, the dramatic purpose of his introduction isn't to make a statement about the kind of character he is. It's to show a young man in the anguish of first love that will quickly be tested. This speaks again to that issue of trust that develops between a writer like Shakespeare and his audience,