Be obsessed by man β stifling bore! (5,2)
I believe the answer is:
dwell on
'be obsessed by' is the definition.
(to dwell on something is to obsess about it)
'man stifling bore' is the wordplay.
I cannot quite see how this works, but
'man' could be 'lon' and 'lon' is present in the answer.
This explanation may well be incorrect...
(Other definitions for dwell on that I've seen before include "Mull over" , "Think at length about" , "Speak at length about" , "Ponder about" , "Linger over" .)