Graeme is not a problem for a close group of three (6,1,5)
I believe the answer is:
menage a trois
'a close group of three' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'graeme is not a problem' is the wordplay.
'problem' indicates an anagram.
'graeme'+'is'+'not'+'a'='graemeisnota'
'graemeisnota' anagrammed gives 'MENAGE A TROIS'.
'for' is the link.
Can you help me to learn more?
(Other definitions for menage a trois that I've seen before include "third party involvement?" , "household of unusual size" , "Complicated household relationship (two + one)" , "triangular arrangement" , "complicated arrangement!" .)