Join a former partner collecting news (5)
I believe the answer is:
annex
'join' is the definition.
(I've seen this before)
'a former partner collecting news' is the wordplay.
'former partner' becomes 'ex'.
'collecting' is an insertion indicator.
'news' becomes 'nn' (I've seen this in other clues).
'a'+'ex'='aex'
'aex' placed around 'nn' is 'ANNEX'.
(Other definitions for annex that I've seen before include "Add to one's territory" , "Append" , "Tack on" , "Extension to a main building" , "Grab" .)