Not bound to be promiscuous (5)
I believe the answer is:
loose
I believe this clue is a double definition.
'not bound' is the first definition.
(I've seen this before)
'promiscuous' is the second definition.
(loose can mean promiscuous)
'to be' is the link.
(Other definitions for loose that I've seen before include "untidy" , "Not secured" , "Lax - inaccurate - unbound" , "Unconfined" , "Unrestricted" .)