These lines from Romeo and Juliet occur in Act three, scene five. Juliet has just spent the entire night with Romeo, following their marriage. When Lady Capulet arrives very early that morning, she unexpectedly announces that Juliet's father has agreed to Paris' proposal, and the couple will marry next Thursday. Juliet does not take the news well, and when Juliet's father enters the scene and sees her tears, he is both unmoved and unsympathetic.
Juliet pleads with her mother to help her delay the marriage, complete with the teenage argument of 'I'll die if I have to do that...' "That dim monument where Tybalt lies" is a tomb. Remember, her cousin Tybalt just died. Juliet threatens her mother that if this unwanted marriage is not postponed, then Juliet might as well join Tybalt in the tomb. Death is preferable over marriage to Paris.