Sadly Liberal brought into sober group ultimately drinks (4)
I believe the answer is:
alas
'sadly' is the definition.
(I've seen this before)
'liberal brought into sober group ultimately drinks' is the wordplay.
'liberal' becomes 'l' (abbreviation).
'brought into' is an insertion indicator.
'sober group' becomes 'aa' (short for Alcoholics Anonymous).
'ultimately' indicates one should take the final letters.
The last letter of 'drinks' is 's'.
'l' inserted into 'aa' is 'ala'.
'ala'+'s'='ALAS'
(Other definitions for alas that I've seen before include "Sad to say!" , "Archaic exclamation of sorrow or regret" , "Expression of grief/pity" , "'- Poor Yorick' (Hamlet)" , "Oh dear!" .)