Lucky for us, we know exactly who the speaker of this poem is, because it comes to us in the form of a song from Jonson's play, Cynthia's Revels.
And, lucky for us, we know a lot about her already, through the sad story of Echo and Narcissus. In Greek mythology, she was a nymph, one of many minor female deities who lived in the forest and spent lots of time dancing and singing. Sounds like a nice life, right? And indeed it was, until one day, she fell in love and everything went to pot. Sigh. Isn't that always how it goes?