Occupant getting in with a partner (6)
I believe the answer is:
inmate
'occupant' is the definition.
(inmate is a kind of occupant)
'in with a partner' is the wordplay.
'with' means one lot of letters go next to another.
'a partner' becomes 'mate' ('mate' can be a synonym of 'partner'**).
'in'+'mate'='INMATE'
'getting' is the link.
(Other definitions for inmate that I've seen before include "eg Prisoner" , "Person confined to institution" , "Cell resident" , "One living in (prison)" , "Occupant" .)