Love affair upset Cameron (7)
I believe the answer is:
romance
'love affair' is the definition.
(I know that love affair can be written as romance)
'upset cameron' is the wordplay.
'upset' indicates anagramming the letters.
'cameron' anagrammed gives 'ROMANCE'.
(Other definitions for romance that I've seen before include "Amorous relationship" , "Feeling of mystery; love affair" , "Cameron (anag) - love story" , "mysterious quality" , "(Wonderful) piece of fiction" .)