Banish former partner over occupation about sex (9)
I believe the answer is:
extradite
'banish' is the definition.
(banish to another country)
'former partner over occupation about sex' is the wordplay.
'former partner' becomes 'ex' (an ex-partner).
'over' says to put letters next to each other.
'occupation' becomes 'trade' (trade is a kind of occupation).
'about' means one lot of letters goes inside another.
'sex' becomes 'it' (a common euphemism).
'trade' going around 'it' is 'tradite'.
'ex'+'tradite'='EXTRADITE'
(Other definitions for extradite that I've seen before include "Send home" , "Bring from abroad" , "Hand over to a foreign jurisdiction" , "Hand over for trial to another government" , "Hand over abroad" .)