Regretting devastation before end of bombing (5)
I believe the answer is:
ruing
'regretting' is the definition.
('rue' can be a synonym of 'regret')
'devastation before end of bombing' is the wordplay.
'devastation' becomes 'ruin' (ruin is a kind of devastation).
'before' means one lot of letters go next to another.
'end of' says to take the final letters.
The last letter of 'bombing' is 'g'.
'ruin'+'g'='RUING'
(Other definitions for ruing that I've seen before include "full of remorse?" , "Bitterly regretting" , "Regretful" , "Feeling bad" , "feeling remorse" .)