Have a crush on the ostentatious (5)
I believe the answer is:
fancy
I believe this clue is a double definition.
'have a crush on' is the first definition.
(I've seen this before)
'the ostentatious' is the second definition.
(thesaurus)
(Other definitions for fancy that I've seen before include "Imagine - whim - highly decorated" , "An ornamental whim?" , "Highly-decorated; whim" , "Imagine; expensive" , "Imagine - find attractive" .)