He seeks perfection, but it's different after I do business (8)
I believe the answer is:
idealist
'he seeks perfection' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'it's different after i do business' is the wordplay.
'different' indicates anagramming the letters (letters placed in a different order).
'after' is a charade indicator (letters next to each other).
'do business' becomes 'deal' (as in dealing with another business).
'its' is an anagram of 'ist'.
'i'+'deal'='ideal'
'ist' after 'ideal' is 'IDEALIST'.
'but' acts as a link.
Can you help me to learn more?
(Other definitions for idealist that I've seen before include "philosopher" , "Person with high and unselfish standards" , "One who aims for perfection, may be unrealistic" , "An optimist or romantic" , "One seeking perfection" .)