Key, before work, to find close friend (5,3)
I believe the answer is:
alter ego
'close friend' is the definition.
'key before work' is the wordplay.
'key' becomes 'alt' (I've seen this in other clues**).
'before' becomes 'ere' (usually literary).
'work' becomes 'go' ('go' can be a synonym of 'work').
'alt'+'ere'+'go'='ALTER EGO'
'to find' is the link.
(Other definitions for alter ego that I've seen before include "Go, relate to other self" , "'One's second self (5,3)'" , "Is it Kent" , "Similar character" , "One's secondary personality" .)