Show up with old lover's model (6)
I believe the answer is:
expose
'show up' is the definition.
(I've seen this before)
'with old lover's model' is the wordplay.
'with' is a charade indicator (letters next to each other).
'old lover' becomes 'ex' (I've seen this in other clues).
'model' becomes 'pose' ('pose' can be a synonym of 'model').
'ex' put next to 'pose' is 'EXPOSE'.
(Other definitions for expose that I've seen before include "Reveal or unmask" , "Disclose" , "Abandon" , "Lay out to view" , "Make visible or obvious" .)