Sentence:  We very seldom work together on "The Archers", we're rarely in the same episodes, so often we're <WSD>ships that pass in the night</WSD>. 
Meaning of the word marked with <WSD> tags:  Two or more people who encounter one another in a transitory, incidental manner and whose relationship is without lasting significance; two or more people who almost encounter one another, but do not do so.