A coy reference to the problem of employment faced by married people with postdoctoral degrees. (It is a play on the surprisingly difficult three body problem of astronomy.) Academic jobs are hard to get. To get two jobs at one place is even harder.
Sometimes, a couple may find jobs in geographically distinct regions and live apart. This is the long distance relationship problem. Or one of the couple may elect to take a less than ideal career job. The stress is real, and many couples break up after graduate school.