Close friend oddly can't find nothing inside (9)
I believe the answer is:
confidant
'close friend' is the definition.
(I've seen this before)
'oddly can't find nothing inside' is the wordplay.
'oddly' indicates an anagram.
'nothing' becomes 'o' (looks like zero - 0).
'inside' is an insertion indicator.
'cant'+'find'='cantfind'
'cantfind' with letters rearranged gives 'cnfidant'.
'cnfidant' going around 'o' is 'CONFIDANT'.
(Other definitions for confidant that I've seen before include "Close friend entrusted with secrets etc" , "Trusted friend" , "Sharer of secrets" , "intimate" .)