Go to ruin supporting a non-drinker (6)
I believe the answer is:
attend
'go to' is the definition.
('attend' can be a synonym of 'go to')
'ruin supporting a non-drinker' is the wordplay.
'ruin' becomes 'end' (ruin something means to end it).
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'non drinker' becomes 'tt' (Teetotaller abbreviation).
'a'+'tt'='att'
'end' after 'att' is 'ATTEND'.
(Other definitions for attend that I've seen before include "Be there ? pay attention" , "Listen closely" , "minister" , "Concentrate carefully" , "Wait upon or be present" .)