Why does Romeo decide to go to the Capulet party?

In Act I Romeo professes his love for a young lady of the Capulet family named Rosaline.   When Romeo and his cousin Benvolio hear about the party given by the Capulets, Benvolio suggests to Romeo that Rosaline will be at the party.  Although his friends believe that this will not be a love interest that will last for long because the Montagues and the Capulets are bitter enemies and Romeo's love for Rosaline is of courtly love.  When it comes to courtly love the woman is always on a pedestal, she never speaks, she never knows that someone is in love with her, and it is always unrequited.  Because his friends know Romeo's patterns of falling in love with women who are unattainable, it is likely they are trying to make Romeo see that Rosaline is not his true love and so help him to leave his melancholy spirits behind and be happy with his friends.

Romeo's friends try hard to talk him into going to the Capulets' party. Mercutio tells him, "we must have you dance" (1.4.13). He accuses Romeo of being a spoilsport, as well as being overly cautious and "Up to the ears" in a love that is not fulfilling for him (1.4.43). Mercutio goes on a long rant about dreams, and that seems to shake Romeo up, changing the whole mood of the conversation. At this point, Romeo says, 

my mind misgivesSome consequence yet hanging in the starsShall bitterly begin his fearful dateWith this night's revels, and expire the termOf a despised life closed in my breastBy some vile forfeit of untimely death.But he that hath the steerage of my course,Direct my sail.  On, lusty gentlemen.  (1.4.107-114)

In other words, Romeo has a feeling that the party will set his fate into motion and that it will initiate a sequence of events that will end in his own death. However, he says, whoever is in charge of his life's course urges him to go.  And so he calls to his friends to depart, altogether, for the Capulets' house. Thus, it seems as though it is Romeo's premonition of his tragic fate that urges him toward the party; he feels as though he must go there.