A short story or novelette read in a 1960s science fiction magazine, probably If, Tomorrow, or Galaxy.
Much of the galaxy has been colonized by humans. Parasitic aliens from another galaxy that control human bodies have invaded and there is a big interstellar space war with them.
After a space battle an uncontrolled man from the human side and a human girl from the invading side find each other in the wreckage and cooperate to survive, though the man fears the girl might be controlled by one of the aliens. The girl comes from a planet famed for its sexy women before the aliens took it over.
The song "The Minstrel Boy to the War Has Gone" is part of the story and/or the title.