Politician in love trio's outed as a fake (8)
I believe the answer is:
impostor
'a fake' is the definition.
(I know that fake can be written as impostor)
'politician in love trio's outed' is the wordplay.
'politician' becomes 'MP' (Member of Parliament).
'in' indicates putting letters inside.
'love' becomes 'o' (love means zero in tennis).
'outed' indicates anagramming the letters.
'o'+'trios'='otrios'
'otrios' anagrammed gives 'iostor'.
'mp' placed inside 'iostor' is 'IMPOSTOR'.
'as' is the link.
(Other definitions for impostor that I've seen before include "One who isn't what he claims to be" , "One assuming a false character" , "type of triumph for Kipling, for example" , "Fake figure" , "a fraud" .)