The poem reads like a short, wry account of a relationship ending. It starts with a small moment of agreement, the kind that sounds almost domestic: heat will soon appear. That could mean a warming house, or a hint that something stronger, like tension or passion, is on its way. Then the tone drops. The "comfort I married" is dead, which suggests the speaker valued ease and familiarity, and now that is gone.
The final image is the strangest and most memorable. The separation leaves "a cheap custard / with a great channel in it." Custard is soft, sweet, and a bit pathetic when it's cheap, and a channel cut through it suggests something once smooth and whole that has been split open. The comparison is almost funny, which keeps the grief from becoming heavy.
The mood is dry, flat, and quietly sad. The speaker doesn't cry out. He lets an odd, homely picture carry the feeling of emptiness.