Sinful sex involved true lady (8)

I believe the answer is:

adultery

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'sinful sex' is the definition.
'adultery' can be an answer for 'sex' (adultery is a kind of sex). I am not sure about the 'sinful' bit.

'involved true lady' is the wordplay.
'involved' indicates anagramming the letters (involved can mean confusing or complex).
'true'+'lady'='truelady'
'truelady' is an anagram of 'ADULTERY'.

Can you help me to learn more?

(Other definitions for adultery that I've seen before include "frowned-on relations" , "Marital infidelity - try a duel (anag)" , "Affairs" , "form of betrayal" , "Extramarital bedroom antics" .)

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