Act 2 of Shakespeare's Romeo and Juliet is a treasure trove of foreshadowing. It's as if Shakespeare couldn't resist telling us what's going to happen to the star-crossed lovers so that we anticipate every moment of their short lives together.
In act 2, scene 2, the famous balcony scene, Juliet expresses her fear for Romeo's safety:
JULIET: How cam'st thou hither, tell me, and wherefore?
The orchard walls are high and hard to climb,
And the place death, considering who thou art,
If any of my kinsmen find thee here.
. . . If they do see thee, they will murder thee. . . .
ROMEO: I have night's cloak to hide me from their eyes;
And but thou love me, let them find me here.
My life were better ended by their hate
Than death prorogued, wanting of thy love. [2.2.66–82]
Romeo says that he would rather die quickly at the hands of the Capulets than to live a long life without her love. At the end of the play, thinking that Juliet is dead, Romeo chooses to take his own life rather than live without her.
At the end of scene 2, Juliet speaks the words that everyone knows, but not before hinting at what's to come in their relationship.
ROMEO: I would I were thy bird.
JULIET: Sweet, so would I.
Yet I should kill thee with much cherishing.
Good night, good night! Parting is such sweet sorrow,
That I shall say good night till it be morrow. [2.2.195–199]
In Friar Laurence's cell in scene 3, when the Friar agrees to marry Romeo and Juliet, Romeo urges him to marry them as soon as possible.
ROMEO: O, let us hence! I stand on sudden haste.
FRIAR LAURENCE: Wisely, and slow. They stumble that run fast. [2.3.96–97]
Since they first met, Romeo and Juliet have been running very fast into their relationship, which only hastens their deaths.
Back in Friar Laurence's cell a few scenes later, Romeo and Juliet are about to be married. Friar Laurence says he hopes all will be well, and Romeo speaks some fateful words.
FRIAR LAURENCE: So smile the heavens upon this holy act
That after-hours with sorrow chide us not!
ROMEO: Amen, amen! But come what sorrow can,
It cannot countervail the exchange of joy
That one short minute gives me in her sight.
Do thou but close our hands with holy words,
Then love-devouring death do what he dare—
It is enough I may but call her mine. [2.6.1–8]
"Love-devouring death" does, in fact, do "what he dare," and Romeo chooses to end his life to "call her mine" forever.