A fellow lives for handsome young man (6)
I believe the answer is:
adonis
'handsome young man' is the definition.
(I've seen this before)
'a fellow lives' is the wordplay.
'fellow' becomes 'don' (I've seen this before).
'lives' becomes 'is' ('be' can be a synonym of 'live').
'a'+'don'+'is'='ADONIS'
'for' is the link.
(Other definitions for adonis that I've seen before include "Type of male beauty" , "Most 8 Greek youth" , "dandy" , "Extremely handsome young man" , "lovely man" .)