Question

Romeo: “Why then, O brawling love, O loving hate,

Answer 1

He is depressed because Rosaline rejected him.

Romeo is lamenting over his love for Rosaline. He is moping because Rosaline does not love him. In fact, Rosaline has chosen to live a life of celibacy and intends to become a nun, so she will not love any man except God. The last line of the excerpt most clearly states this when he says, "This love feel I, that feel no love in this." He's saying that the love he feels for Rosaline is not returned in love for him.