He's ardent, I fancy, showing crush (10)
I believe the answer is:
dishearten
'crush' is the definition.
'he's ardent i fancy' is the wordplay.
'fancy' is an anagram indicator.
'hes'+'ardent'+'i'='hesardenti'
'hesardenti' is an anagram of 'DISHEARTEN'.
'showing' is the link.
(Other definitions for dishearten that I've seen before include "dismay?" , "Put a damper on" , "Bring down" , "cast down" , "Cause (someone) to lose confidence" .)