In case of doubt, is your husband inside cheating? (9)
I believe the answer is:
dishonest
'cheating?' is the definition.
(I've seen this before)
'in case of doubt is your husband inside' is the wordplay.
'in' is an insertion indicator.
'case of' suggests removing the centre (like emptying a case).
'your' becomes 'ones' (I've seen this in another clue).
'husband' becomes 'h' (abbreviation).
'inside' is an insertion indicator.
'doubt' with its centre taken out is 'dt'.
'is'+'ones'='isones'
'dt' going around 'isones' is 'disonest'.
'disonest' enclosing 'h' is 'DISHONEST'.
(Other definitions for dishonest that I've seen before include "Corrupt" , "Crooked" , "cheating" , "Mendacious like hedonists" , "shifty" .)