Former lover sat bare (7)
I believe the answer is:
'bare' is the definition.
(I've seen this before)
'former lover sat' is the wordplay.
'former lover' becomes 'ex'.
'sat' becomes 'posed' ('pose' can be a synonym of 'sit').
(Other definitions for exposed that I've seen before include "Not hidden" , "Unmasked, revealed" , "in the nude" , "Laid bare" , "Deprived of protection" .)