Sleeping around is out (6)
I believe the answer is:
untrue
I believe this clue is a double definition.
'sleeping around' is the first definition.
(I've seen this before)
'out' is the second definition.
(I've seen this before)
'is' acts as a link.
(Other definitions for untrue that I've seen before include "Not accurate or veracious" , "Counter-factual" , "Not faithful" , "Fallacious" , "Not correct, like a lie" .)