Damages and does wrong to the bitter end (6)
I believe the answer is:
erodes
'damages' is the definition.
(eroding is a kind of damaging)
'does wrong to the bitter end' is the wordplay.
'wrong' indicates an anagram.
'to' is a charade indicator (letters next to each other) (I've seen this in other clues).
'end' suggests the final letters.
The final letters of 'the bitter' are 'er'.
'does' with letters rearranged gives 'odes'.
'odes' after 'er' is 'ERODES'.
'and' is the link.
(Other definitions for erodes that I've seen before include "Wears away as by time or water" , "Wears away with weather" , "Eats away" .)