why is Duke orsino depressed at the beginning of twelfth night? why is he listening to music?

The Duke is rather a tense guy at the beginning of the play. He has this band that keeps plucking out the tunes to ease his jangled nerves and puts him in the mood for some love action! THen he gets all depressed and tells the band to get lost. The reason seems to be his unrequited love, thus far, for the fair Olivia.