The first major event in Act 3 of Romeo and Juliet is the fight between Tybalt and Mercutio, leading to Mercutio's death as well as Tybalt's. Act 3, Scene 1 opens with Benvolio begging Mercutio to get off the street, arguing, "The day is hot, the Capulets abroad / And if we meet, we shall not scape a brawl" (2-3). However, Mercutio refuses to listen and they are soon approached by Tybalt who is looking to challenge Romeo to a duel. When Romeo refuses, Mercutio challenges Tybalt for insulting Romeo, leading to his own death. Romeo then revenges Mercutio's death by killing Tybalt.
The second event is that Juliet learns of Tybalt's death, which leads to a moment of revelation. Juliet believes for the first time that she cannot trust Romeo, but, like an adult, convinces herself not to think badly of her husband and to continue supporting him. Simultaneously, Romeo is sentenced to banishment by Prince Escalus and goes crying to Friar Laurence. Friar Laurence chastises Romeo for acting like a crying woman and tells him to rejoice that he is still alive and to go and comfort his wife.
In Scene 4, which is later that night, we see Paris visit Lord Capulet to extend his sympathy for the death of Tybalt and to find out if Juliet has consented to marry him, saying to Lady Capulet, "Madam, good night. Commend me to your daughter" (7). Lord Capulet decides that the best way to ease his daughter's seemingly extreme grief over Tybalt is to give her a happy wedding day and gives his consent to allow Paris to marry her.
Finally, Romeo and Juliet consummate their marriage and Romeo leaves to fulfill his punishment of banishment in Mantua. Juliet is informed by her parents that she is expected to marry Paris on Thursday, two days from that same morning that Romeo leaves. The act closes with Juliet refusing to marry Paris and being threatened by her parents to be disowned if she does not.