Your question is not very specific, so I am going to assume that the scene you are refering to is Act I scene 2, when Romeo confesses to Benvolio what is bothering him and how he talks about his love-sick state thanks to his infatuation with Rosaline. It is this that is causing his aloof attitude and behavioiur. However, serendipitously (or perhaps not given the outcome), at this moment a servant comes announcing the ball that is to be held at the Capulet's house that night, and Benvolio thus proposes his solution to Romeo's melancholy state:
At this same ancient feast of Capulet's
Sups the fair Rosaline whom thou so loves;
With all the admired beauties of Verona.
Go thither, and with unattainted eye
Compare her face with some that I shall show,
And I will make thee think thy swan a crow.
Thus Benvolio suggests that they go to the ball, and that there he will point out women who are far more beautiful than Rosaline, thus curing Romeo of his love-sick state and his infatuation with her.