Not living together may be a factor (5)
I believe the answer is:
apart
'not living together' is the definition.
(I've seen this before)
'a factor' is the wordplay.
'factor' becomes 'part'.
'a'+'part'='APART'
'may be' is the link.
(Other definitions for apart that I've seen before include "Cut off - in pieces" , "set aside" , "In pieces; separate" , "Separated physically" , "Separated; to one side" .)