Former wife playing tough (8)
I believe the answer is:
exacting
'tough' is the definition.
(I've seen this before)
'former wife playing' is the wordplay.
'former wife' becomes 'ex'.
'playing' becomes 'acting' ('act' can be a synonym of 'play').
'ex'+'acting'='EXACTING'
(Other definitions for exacting that I've seen before include "Making great demands, requiring real effort" , "Requiring hard work and attention" , "Requiring great effort, arduous" , "Meticulous" , "Demanding much" .)