Blessed fellow dated you — a sore point! (4)
I believe the answer is:
stye
'a sore point' is the definition.
'blessed fellow dated you' is the wordplay.
'blessed fellow' becomes 'st' (abbreviation for saint).
'dated you' becomes 'ye' (historical or dated form of 'you').
'st'+'ye'='STYE'
(Other definitions for stye that I've seen before include "Eyelid problem" , "swelling by organ" , "Swelling near the eye" , "Infection on the edge of the eye" , "Animal pen" .)