Agreement in romantic relationship beginning to disappear (8)

I believe the answer is:

alliance

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'agreement' is the definition.
(I know that alliance is a type of agreement)

I don't understand the rest of the clue.

(Other definitions for alliance that I've seen before include "The joining by political agreement or treaty" , "Formal agreement" , "League - treaty" , "A joining of forces" , "Bond" .)

I've seen this clue in The Independent.

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