Someone you once dated, handsome model (7)
I believe the answer is:
example
'model' is the definition.
(I know that model can be written as example)
'someone you once dated handsome' is the wordplay.
'someone you once dated' becomes 'ex' (ex-partner).
'handsome' becomes 'ample' (handsome can mean ample or plenty).
'ex'+'ample'='EXAMPLE'
(Other definitions for example that I've seen before include "not the actual version" , "Characteristic item" , "Illustrative case" , "Standard" , "Prototype" .)