With companion, I again occupy the apartment (6)
I believe the answer is:
paired
'with companion i again occupy the apartment' is the definition.
I can't tell whether this definition defines the answer.
'i again occupy the apartment' is the wordplay.
'again' becomes 're' (prefix meaning 'again').
'occupy' indicates putting letters inside (inserted letters occupy or enter the word).
'the apartment' becomes 'pad' (I've seen this in another clue).
'i'+'re'='ire'
'ire' inserted inside 'pad' is 'PAIRED'.
Can you help me to learn more?
(Other definitions for paired that I've seen before include "Were mates" , "'Coupled, matched (6)'" .)