Entering affair, former lover's yielding (7)

I believe the answer is:

flexing

'yielding' is the definition.
(bending or changing shape under pressure)

'entering affair former lover's' is the wordplay.
'entering' means one lot of letters goes inside another.
'affair' becomes 'fling' (I have seen 'Brief affair' mean 'fling' so perhaps 'affair' could also mean 'fling').
'former lover' becomes 'ex'.
'fling' enclosing 'ex' is 'FLEXING'.

(Another definition for flexing that I've seen is " getting tense".)

I've seen this clue in The Telegraph.

Want a hint initially instead of a full solution? Install my app