'Item I gyve unto my wife my second best bed ...' (from Shakespeare's will) (epigraph)
The poem begins with the facts. In his will, Shakespeare left his wife his second best bed. Most people interpret this to mean that Shakespeare didn't really love his wife, but Duffy will go on to share a different point of view.
The bed we loved in was a spinning world of forests, castles, torchlight, clifftops, seas where we would dive for pearls. […] (1-3)
Right from the beginning of the poem, Duffy presents us with the idea that there really was a lot of love between Anne Hathaway and Shakespeare. The second best bed is not some broken-down piece of furniture; it's "the bed [they] loved in."
In the other bed, the best, our guests dozed on, dribbling their prose. […] (11-12)
The house guests who sleep in the best bed are boring, "dribbling their prose." Compare this to the magical and romantic poetry that Anne and Shakespeare create in the second best bed.
I hold him in the casket of my widow's head as he held me upon that next best bed. (13-14)
This final couplet is a strong statement in favor of their love. Anne says that she holds onto Shakespeare's memory, just as he once held her in that second best bed. The intense rhyme suggests that this is the final word on the issue (at least from Duffy!).