In literature, apostrophe is a figure of speech sometimes represented by exclamation “O”. so in the poem you can see the representation in "O Attic shape! Fair attitude! with brede " or in poetry, an apostrophe is a figure of speech in which the poet addresses an absent person, an abstract idea, or a thing, so "Bold Lover, never, never canst thou kiss,
Though winning near the goal yet, do not grieve;
She cannot fade, though thou hast not thy bliss,
For ever wilt thou love, and she be fair! "address the "lover" and this practice is found throughout the poem