Man to live with Nancy off and on (5)
I believe the answer is:
benny
'man' is the definition.
'live with nancy off and on' is the wordplay.
'live' becomes 'be' ('be' can be a synonym of 'live').
'with' means one lot of letters go next to another.
'off and on' means one should take alternating letters (letters used at regular intervals).
The alternate letters of 'nancy' are 'nny'.
'be'+'nny'='BENNY'
'to' is the link.
(Other definitions for benny that I've seen before include "--- Hill, saucy comedian" , "-- Hill (TV comedian)" .)