Desire for union to accept current offer, see (6)
I believe the answer is:
libido
'desire for union' is the definition.
'to accept current offer see' is the wordplay.
'to accept' is an insertion indicator.
'current' becomes 'i' (symbol for electric current).
'offer' becomes 'bid' ('bid' can be a synonym of 'offer').
'see' becomes 'lo' (archaic word meaning 'look!').
'i'+'bid'='ibid'
'ibid' put inside 'lo' is 'LIBIDO'.
(Other definitions for libido that I've seen before include "Emotional craving" , "Emotional energy associated with sexual desire" , "Instinctive desire" , "Natural urges" , "Life force" .)