Old flame joining French island émigré (5)
I believe the answer is:
exile
'emigre' is the definition.
(I've seen this in another clue)
'old flame joining french island' is the wordplay.
'old flame' becomes 'ex' (a former partner).
'joining' means one lot of letters go next to another.
'french island' becomes 'ile' ('island' in French).
'ex'+'ile'='EXILE'
(Other definitions for exile that I've seen before include "Banishment from home" , "being always away from home" , "forced to leave" , "Expulsion from one's country" , "officially banish" .)