In autumn, we're suffering for so long! (8)
I believe the answer is:
farewell
'so long' is the definition.
(I've seen this before)
'in autumn we're suffering' is the wordplay.
'in' means one lot of letters goes inside another.
'autumn' becomes 'fall' (synonyms).
'suffering' is an anagram indicator.
'were' is an anagram of 'rewe'.
'fall' enclosing 'rewe' is 'FAREWELL'.
'for' is the link.
(Other definitions for farewell that I've seen before include "Cape at the southernmost point of Greenland" , "Archaic goodbye or leave-taking" , "Archaic goodbye - good luck" , "It may be said when 15" , "All the best" .)