Hopelessness from couple after diet's regularly ignored (7)
I believe the answer is:
despair
'hopelessness' is the definition.
(despair is a kind of hopelessness)
'couple after diet's regularly ignored' is the wordplay.
'couple' becomes 'pair' (synonyms).
'after' says to put letters next to each other.
'regularly ignored' indicates alternate letters (letters removed at regular intervals).
The alternating letters of 'diets' are 'des'.
'pair' after 'des' is 'DESPAIR'.
'from' acts as a link.
(Other definitions for despair that I've seen before include "Total loss of hope" , "sort of counsel?" , "displaying lack of optimism" , "First appearance" , "Complete absence of hope" .)