Love affair in the Catholic church (7)
I believe the answer is:
romance
'love affair' is the definition.
('romance' can be a synonym of 'love affair')
'catholic church' is the wordplay.
'catholic' becomes 'roman' (Roman Catholic is an example).
'church' becomes 'ce' (abbreviation for Church of England).
'roman'+'ce'='ROMANCE'
'in the' acts as a link.
(Other definitions for romance that I've seen before include "Amorous relationship" , "Love affair; medieval tale" , "fairy story?" , "marriage?" , "Cameron (anag) - love story" .)