“Good Night, Good night! Parting is such sweet sorrow, that I shall say good night till it be morrow”

These comments are spoken by Juliet after a lengthy sequence in which they proclaim their love but must now part ways. Juliet says, "Good Night, Good night! Parting is such sweet sorrow, that I shall say good night till it be morrow” which is regarded as one of the play's most famous lines. Simply put, parting between lovers is both sweet and painful because of the time spent together.

Romeo and Juliet, as lovers, are eagerly anticipating their reunion. Juliet makes her goodbyes to her boyfriend, Romeo, at this moment, expecting another reunion the next day. This is Juliet's way of saying goodnight to Romeo, her boyfriend. This sad separation brings them joy and appears "sweet" since it gives them hope of seeing one other the next morning. She mentions the agony they've been through since their relationship began. The same is true for Juliet, since saying farewell to Romeo brings up strong feelings in her; yet, melancholy reminds her of their profound love, therefore it is sweet. She wants to say goodbye to him again and over till daylight. Simply said, couples despise being separated from one another when they are really in love.

Juliet - Act 2, Scene 2.