Lover dropped in — see TV set that's wide (9)
I believe the answer is:
extensive
'wide' is the definition.
(I know that wide can be written as extensive)
'lover dropped in see tv set' is the wordplay.
'lover dropped' becomes 'ex' (ex-partner).
'set' is an anagram indicator (instruction to set the letters).
'in'+'see'+'tv'='inseetv'
'inseetv' anagrammed gives 'tensive'.
'ex'+'tensive'='EXTENSIVE'
'that's' is the link.
(Other definitions for extensive that I've seen before include "Broad in scope" , "Comprehensive" , "Covering much area" , "Exist even being wide-ranging" , "Far-reaching, wide" .)