Why is romeo in romeo and Juliet not in the mood for the party act 1 scene 4?

In Act 1, Scene 4 of "Romeo and Juliet," Romeo is in a somber mood because he is still heartbroken over his unrequited love for Rosaline. He tells his friends that he has a sense of foreboding about the party and worries that the night's events will lead to something unfortunate.