The speaker describes himself in strange, dreamlike images, and the title gives the key: he is "cold hearted." He calls himself husband to a boat, a partner that belongs to water and drifts, and then says he is the ice, the thing that can freeze a boat in place. Marriage and coldness sit side by side, so the relationship feels both committed and chilly.
The next lines shift. He changes "like the afternoon," slowly and without effort, as if his moods are just part of the day's light. Then he is "putting things in order" in a castle on Mars. That is a tidy, controlled place, but also remote, lifeless and far from anyone else.
The speaker doesn't seem to be in anguish. His tone is calm, almost matter-of-fact, which makes the poem more unsettling. The mood is detached, quiet and lonely, a portrait of someone who has arranged his life neatly but kept himself out of reach.