Life with former partner is strained we hear (9)
I believe the answer is:
'life' is the definition.
(I've seen this before)
'former partner is strained we hear' is the wordplay.
'former partner' becomes 'ex' (an ex-partner).
'strained' becomes 'tense' (similar in meaning).
'we hear' shows a homophone (sound like).
'tense' sounds like 'tence'.
'with' is the link.
(Other definitions for existence that I've seen before include "A way of living" , "Way of life" , "State of being" , "The business of being" , "survival" .)