The ex, after breaking up, does get lonely (8)
I believe the answer is:
desolate
'lonely' is the definition.
(thesaurus)
'the ex after breaking up does' is the wordplay.
'the ex' becomes 'late' (I've seen this in other clues).
'after' is a charade indicator (letters next to each other).
'breaking up' is an anagram indicator.
'does' is an anagram of 'deso'.
'late' after 'deso' is 'DESOLATE'.
'get' is the link.
(Other definitions for desolate that I've seen before include "upset" , "Wretched, unhappy" , "extremely sad" , "alone" , "Bleak, dismal; wretched" .)