It's lengthened for former partner, cared for (8)
I believe the answer is:
extended
'it's lengthened' is the definition.
(extending is a kind of lengthening)
'former partner cared for' is the wordplay.
'former partner' becomes 'ex' (an ex-partner).
'cared for' becomes 'tended' (I've seen this in another clue).
'ex'+'tended'='EXTENDED'
'for' is the link.
(Other definitions for extended that I've seen before include "Stretched or reached out - the hand of friendship? (8)" , "Stretched out over a distance" , "Made longer" , "Stretched, drew out" , "Reached out for next deed" .)