Answer:
Romeo was in a melancholy mood when he came to the Capulet's home for a feast and this is because of the fair Rosaline who he fancies himself to be in love with. Coming to the Capulet's home despite the enmity between his family and theirs is a risk on its own, getting to meet Juliet and falling in love with her is the greatest risk to him.
If he didn't go for the feast he wouldn't have met Juliet and the tragedy would have been averted but fate has other plans for the two star crossed lovers.
He came to the feast for Rosaline but left with Juliet in his thoughts.
