Originally, Gauguin left relationship for fascinating beauty (7)
I believe the answer is:
glamour
'fascinating beauty' is the definition.
(I've seen this before)
'originally gauguin left relationship' is the wordplay.
'originally' suggests taking the first letters.
'relationship' becomes 'amour' (amour is a kind of relationship).
The first letters of 'gauguin left' is 'gl'.
'gl'+'amour'='GLAMOUR'
'for' is the link.
(Other definitions for glamour that I've seen before include "Charm and allure" , "Beauty created by clothes and make-up" , "Alluring quality" , "Voluptuous allure" , "Appealing and beautiful quality" .)