Two thirds of models fall hopelessly for past lover (3,5)

I believe the answer is:

old flame

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'past lover' is the definition.
(an old flame is a former lover)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for old flame that I've seen before include "Former sweetheart" , "Someone once loved" , "Ex" , "Former lover" , "Former partner" .)

I've seen this clue in The Guardian.

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