Partner mostly upset about wife in European city (7)
I believe the answer is:
antwerp
'european city' is the definition.
(I've seen this before)
'partner mostly upset about wife' is the wordplay.
'mostly' means to remove the last letter.
'upset' indicates an anagram.
'about' indicates putting letters inside.
'wife' becomes 'w' (abbreviation).
'partner' with its final letter taken away is 'partne'.
'partne' is an anagram of 'anterp'.
'anterp' placed around 'w' is 'ANTWERP'.
'in' is the link.
(Other definitions for antwerp that I've seen before include "Van Dyck birthplace" , "foreign city" , "Busy Belgian port" , "War-damaged city" , "North Sea port" .)