Former partner crept out of passage (7)
I believe the answer is:
excerpt
'passage' is the definition.
(I know that excerpt is a type of passage)
'former partner crept out' is the wordplay.
'former partner' becomes 'ex' (an ex-partner).
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'crept' is an anagram of 'cerpt'.
'ex'+'cerpt'='EXCERPT'
'of' is the link.
(Other definitions for excerpt that I've seen before include "A passage from, music or book" , "Passage taken from book etc" , "Piece of work" , "part of programme" , "Literary taste" .)