After Romeo and Juliet are married, and Romeo is banished for killing Mercutio, the Capulets arrange for Juliet to marry Paris. This arrangement has been in the making for awhile, but up to this point the Capulets felt that Juliet was too young. Juliet is basically commanded to marry Paris, even though she expresses to her mother that she does not want to marry him. The Nurse, knowing that Juliet is married to Romeo, still encourages Juliet to make this new match, thinking that the outcome will be better.
At the beginning of the play, the Chorus tells the audience that these are star-crossed lovers. At this point in the play, the audience sees the extent of the tragedy. Juliet would rather fake her death and never again see her family than betray her love to Romeo. They have reached the point of no turn, and every decision brings them closer to the tragic end.