Can cut back - or try last group in the sack? (9)

I believe the answer is:

polyamory

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'try last group in the sack?' is the definition.
I don't know anything about this answer so I cannot tell whether it can be defined by this definition.

'can cut back or' is the wordplay.
I cannot quite see how this works, but
'or' is within the answer.
This may be the basis of the clue (or it may be nonsense).

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I've seen this clue in the Sydney Morning Herald.

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