Kinky games are not restricting one in relationship (6,1,5)
I believe the answer is:
menage a trois
'relationship' is the definition.
(relationship involving three people)
'kinky games are not restricting one' is the wordplay.
'kinky' is an anagram indicator.
'restricting' means one lot of letters goes inside another.
'one' becomes 'I' (Roman numeral).
'games'+'are'+'not'='gamesarenot'
'gamesarenot' anagrammed gives 'menageatros'.
'menageatros' enclosing 'i' is 'MENAGE-A-TROIS'.
'in' acts as a link.
(Other definitions for menage a trois that I've seen before include "triangular arrangement" , "third party involvement?" , "complicated arrangement!" , "household of unusual size" , "Triangular relationship(s)" .)