Echo understood about Narcissus finally — he loves himself (7)
I believe the answer is:
egotist
'he loves himself' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'echo understood about narcissus finally' is the wordplay.
'echo' becomes 'e' (phonetic alphabet: alpha, bravo, charlie etc.).
'understood' becomes 'got' (getting is a kind of understanding).
'about narcissus' becomes 'ist' (I can't explain this - if you can you should believe this answer much more).
'finally' is a charade indicator (letters next to each other) (some letters go at the end of others).
'e'+'got'+'ist'='EGOTIST'
Can you help me to learn more?
(Other definitions for egotist that I've seen before include "Self-conceited person" , "Conceited and self-centred person" , "braggart" , "Self-obsessed individual" , "Bighead" .)