Live with former partner first ... (5)
I believe the answer is:
exist
'live' is the definition.
(synonyms)
'with former partner first' is the wordplay.
'with' says to put letters next to each other.
'former partner' becomes 'ex'.
'first' becomes 'ist'.
'ex' next to 'ist' is 'EXIST'.
(Other definitions for exist that I've seen before include "Subsist" , "quick!" , "Have being or continue living" , "Survive" , "Be alive" .)