O, the apostrophe, how we love thee!
The speaker could be addressing an abstract concept like love, a person (dead or alive), a place, or even a thing, like the sun or the sea.
Check out William Wordsworth's sonnet "London, 1802" for an apostrophe to (the much older and way dead poet) John Milton. Emily Dickinson also has a lot of apostrophes in her poetry, like the one to summer in "The gentian weaves her fringes". Can you spot the apostrophe?