Speak well of former lover to first lover (5)
I believe the answer is:
extol
'speak well of' is the definition.
(I've seen this before)
'former lover to first lover' is the wordplay.
'former lover' becomes 'ex' (an ex-lover).
'first lover' becomes 'l' (1st letter of 'lover').
'ex'+'to'+'l'='EXTOL'
(Other definitions for extol that I've seen before include "Highly rate" , "be lavish with praise" , "Magnify" , "Speak highly" , "Highly commend" .)