Revealing former spouse, sitting (8)
I believe the answer is:
exposing
'revealing' is the definition.
('expose' can be a synonym of 'reveal')
'former spouse sitting' is the wordplay.
'former spouse' becomes 'ex' (an ex-spouse).
'sitting' becomes 'posing' (synonyms).
'ex'+'posing'='EXPOSING'
(Other definitions for exposing that I've seen before include "Uncovering" , "outing" , "Showing up" , "Subjecting to light, making known" .)