Fail to admit love, being vague (5)
I believe the answer is:
loose
'vague' is the definition.
(I've seen this before)
'fail to admit love' is the wordplay.
'fail' becomes 'lose' (I've seen this in other clues).
'to admit' is an insertion indicator.
'love' becomes 'o' (In tennis, 'love' means 'zero').
'lose' enclosing 'o' is 'LOOSE'.
'being' is the link.
(Other definitions for loose that I've seen before include "Water heater" , "Unfixed" , "escaped!" , "Not strict" , "Liberal" .)