He and I are inseparable (7)
I believe the answer is:
egotist
'he and i are inseparable' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he' is the wordplay.
I cannot really understand how this works, but
'he' could be 'otis' (I've seen this before) and 'otis' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for egotist that I've seen before include "show-off" , "A self-absorbed and conceited person" , "Self-obsessed person" , "one promotes oneself" , "Self-conceited person" .)