I am in rooms with him (5)
I believe the answer is:
denis
'him' is the definition.
'i am in rooms' is the wordplay.
I cannot really see how this works, but
'i' is found in the answer.
'rooms' could be 'dens' (den is a kind of room) and 'dens' is found in the remaining letters.
No letters remain.
This explanation may well be incorrect...
'with' acts as a link.
Can you help me to learn more?
(Other definitions for denis that I've seen before include "St -, first Paris bishop" , "- Healey, former Chancellor of the Exchequer" , "Patron saint of France" .)