I go - unionism turned out to be humiliating (11)
I believe the answer is:
ignominious
'to be humiliating' is the definition.
(I've seen this before)
'i go unionism turned' is the wordplay.
'turned' indicates an anagram.
'go'+'unionism'='gounionism'
'gounionism' anagrammed gives 'gnominious'.
'i'+'gnominious'='IGNOMINIOUS'
'out' acts as a link.
(Other definitions for ignominious that I've seen before include "Abject" , "Deserving public disgrace" , "Causing disgrace" , "Shameful, disgraceful" , "Deserving disgrace or shame" .)