There may be a spare seat when a married person does this (9)
I believe the answer is:
separates
'there may be a' is the definition.
I can't judge whether this definition defines the answer.
'spare seat when a married person does this' is the wordplay.
'spare seat' can be anagrammed to 'SEPARATES'.
But, I'm not sure how the anagram is indicated.
Can you help me to learn more?
(Other definitions for separates that I've seen before include "Breaks up" , "Splits up, sunders" , "Keeps apart from others" , "Detaches from another" , "Sorts out" .)