Letters exchanged before couple finally move (8)
I believe the answer is:
resettle
'move' is the definition.
(I've seen this in another clue)
'letters exchanged before couple finally' is the wordplay.
'exchanged' indicates an anagram.
'before' means one lot of letters go next to another.
'finally' says to take the final letters.
The final letter of 'couple' is 'e'.
'letters' is an anagram of 'resettl'.
'resettl'+'e'='RESETTLE'
(Other definitions for resettle that I've seen before include "Take up living in a different place" , "Take up residence in a different place" , "Move home" , "Move to live in a different place" , "put down new roots" .)