Three short lines hold a whole one-sided relationship. The speaker says their heart talks with someone "every day," which suggests a bond that hasn't ended, at least on their side. But the conversations seem to happen only inside the speaker's head. Out in the real world, there is silence.
That gap is what the poem is about. The phrase "what could have been" points to a love or friendship that never became, or no longer is, what the speaker hoped for. They are "holding on," and the words sound tired, as if letting go would be easier but isn't possible yet. The silence doesn't just exist; it "fills the space between us," as though it has taken up the room where words used to be.
The mood is quiet, wistful, and a little lonely. There's no anger here, only longing and a stubborn kind of hope. The title "Voices" adds an ache: the only voices we can be sure of are the ones the speaker imagines.