Death is hanging over this poem like a big ol' Harry Potter-style Dementor, sucking any shred of joy or happiness out of it. The speaker spends the whole poem wallowing in grief—both for the death of his beloved, and for their love which was imperfect while she was living. He's got some confusing emotions going on, and he's having trouble interpreting his reality. His grief is making him just a little unhinged (if not out-and-out insane). Whether or not you believe in ghosts (or, for that matter, the poem believes in ghosts) we can't help but notice that the speaker is having some trouble answering basic questions. Does he hear the voice of his dead beloved? Or the wind? Is this really a difficult question? Death, the poem seems to suggest, troubles the minds of us all.
No ghosts here, gang. The speaker's grief over his wife's death has driven him to madness.
The voice of the woman is totally real—she's a ghost! This poem believes in the afterlife.