Around 1993-1994, certainly no later than the end of 1994, I purchased a paperback from a thrift store on Nantucket. The cover was black; the title (in large white letters under a circular graphic) was two very short words, possibly with a "II" at the end, as this was a sequel to a previous book. I'm almost sure the first word was "Star"; I thought the second word was "Cops" but that only turns up information about the 1987 BBC2 TV series. The cover design including the typography made me think the book was printed in the late 1970s or early-to-mid-1980s.
The two main characters travelled around space in their own spaceship; I believe they were official agents for some kind of peacekeeping force.
The man was called a a "human bullet" or something similar; I got the impression that this was something like calling him a "paratrooper", designating the specific skill-set he brought to his occupation.
The woman was what would today be called a "catgirl" (though I don't remember if the book used that term): a humanoid with visible feline traits.
The only part of the plot I remember was the somewhat surprising denouement when they retired and settled down as a couple, possibly even expecting a child. It was surprising because I hadn't perceived much of a romantic relationship between them prior to that.
Can anyone identify this?