Attracted by wife-swapping? Naughtily aroused - and ultimately participating! (10)
I believe the answer is:
adulterous
'participating' is the definition.
Both the answer and definition are adjectives. Perhaps you can see a link between them that I can't see?
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for adulterous that I've seen before include "Betraying a legal partner" , "untrue" .)