A painful break, in any case (5)
I believe the answer is:
agony
'case' is the definition.
The answer and definition can be both states of affairs as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'a painful break in any' is the wordplay.
'a painful break' becomes 'go' (synonyms. I am not sure about the 'painful' bit.).
'in' means one lot of letters goes inside another.
'go' inserted within 'any' is 'AGONY'.
Can you help me to learn more?
(Other definitions for agony that I've seen before include "This aunt answers readers' questions" , "Suffering - anguish" , "Great pain or suffering" , "Extreme suffering - kind of aunt" , "Excruciating pain" .)