By outward appearances, the man looks like he has it all. He is in a relationship, and probably seems well off within the trappings of a successful life. His lover is very committed to him. Yet something eats away at him and he is neither satisfied nor happy. Quite to the contrary, he feels out of control - like he is going "down the drain;" and he cannot control it because his life has assumed its own trajectory. His "body spins and sinks" like a rock tossed into deep murky water. His only escape is to fall asleep, but sleep merely throws him "into a black hole." From a black hole to sinking and being sucked down a drain, all of the imagery of this poem suggests someone unable to resist the overwhelming pull of gravity sucking him toward an undesirable existence.
The things that should be pleasant for the man - sex and love - are more like drudgery and chores. Sex makes him "feel like a servant." Love makes him "feel like a slave." These things are serving someone else, his master, rather than himself. The imagery of a servant and a slave implies a sense of subordination and a life spent at someone else's pleasure. While his lover thinks the relationship is wonderful, that lover fails to see the one-sidedness of it all. The old notion of a committed lover being shackled with a ball-and-chain comes to mind.