The correct answer is the second one: because Friar Laurence has already married Juliet to Romeo.
After the night that Romeo and Juliet met and made their oath of love, they marry in secrecy at the chapel of Friar Laurence. During the same day, Romeo confronts Tybalt, Juliet's cousin, in a duel to the death and kills him, for which Romeo is exiled from Verona. Misinterpreting Juliet's mourn, her father decides to accept Paris' request to marry her, which creates a dramatic irony as Juliet is already married.
