Become embittered and go off (4,4)
I believe the answer is:
turn sour
'become' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'embittered and go off' is the wordplay.
'embittered' becomes 'sour' (I've seen this before).
'and' is a charade indicator (letters next to each other).
'go off' becomes 'turn' (both can mean to start to rot).
'sour' put after 'turn' is 'TURN SOUR'.
Can you help me to learn more?
(Another definition for turn sour that I've seen is " Become unfavourable".)