Surprisingly ready to accept leaderless cult's extra-marital relations (8)

I believe the answer is:
adultery
'marital relations' is the definition.
(thesaurus)
'surprisingly ready to accept leaderless cult's' is the wordplay.
'surprisingly' is an anagram indicator (a surprising ordering of the letters).
'to accept' is an insertion indicator.
'leaderless' means to remove the first letter.
'ready' anagrammed gives 'adery'.
'cult' with its first letter removed is 'ult'.
'adery' enclosing 'ult' is 'ADULTERY'.
'extra' acts as a link.
This may not be right. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for adultery that I've seen before include "cheating" , "Unfaithfulness to one's spouse" , "Extramarital sex" , "Moral lapse" , "Seventh Commandment infraction" .)
