Those always having potential to rekindle relationships? (3,6)

I believe the answer is:

old flames

'relationships?' is the definition.
Both the definition and answer are plural nouns.
Maybe you can see an association between them that I don't see?

I cannot understand how the remainder of the clue works.

(Another definition for old flames that I've seen is " Former lovers - hot stuff".)

I've seen this clue in The Independent.

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