Ernie goes crazy for this girl (5)
I believe the answer is:
irene
'this girl' is the definition.
(I've seen this before)
'ernie goes crazy' is the wordplay.
'goes crazy' indicates an anagram (I've seen 'going crazy' mean this).
'ernie' anagrammed gives 'IRENE'.
'for' is the link.
(Other definitions for irene that I've seen before include "Representative of peace" , "Greek godess of peace" , "In Greek mythology, the goddess of peace" , "Greek goddess of peace (English name)" , "- - Worth, actress" .)