Union supporter is faithful first (8)
I believe the answer is:
loyalist
'union supporter' is the definition.
'loyalist' can be an answer for 'supporter' (loyalist is a kind of supporter). I am unsure of the 'union' bit.
'faithful first' is the wordplay.
'faithful' becomes 'loyal' (similar in meaning).
'first' becomes 'ist' (ist resembles 1st).
'loyal'+'ist'='LOYALIST'
'is' is the link.
Can you help me to learn more?
(Other definitions for loyalist that I've seen before include "One staying in support of a ruler or government" , "One true to monarch or government" , "supporter of British rule?" , "Patriot" , "Government supporter, cavalier changing sides" .)