Be clear about former spouse starting as appalling (9)
I believe the answer is:
execrable
'appalling' is the definition.
(I've seen this before)
'be clear about former spouse starting' is the wordplay.
'about' indicates an anagram.
'former spouse' becomes 'ex' (an ex-spouse).
'starting' says to put letters next to each other.
'be'+'clear'='beclear'
'beclear' anagrammed gives 'ecrable'.
'ecrable' put after 'ex' is 'EXECRABLE'.
'as' acts as a link.
(Other definitions for execrable that I've seen before include "Accursed" , "Woeful" , "Awful" , "Appalling, abhorrent" , "Abominable, deserves to be detested" .)