Threesome in rude relations tangle messily rejecting ordered duos (7,8)

I believe the answer is:

eternal triangle

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'threesome' is the definition.
(eternal triangle can mean a love triangle)

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for eternal triangle that I've seen before include "emotional relationship" , "Complex relationship" , "Love relationship between three people" , "sexual relationship" , "In which three lovers" .)

I've seen this clue in The Telegraph.

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