For good measure, not married with new partner (9)
I believe the answer is:
eternally
'for good' is the definition.
(I've seen this before)
'measure not married with new partner' is the wordplay.
I cannot really see how this works, but
'measure' could be 't' (T is an example) and 't' is found in the answer.
'new' could be 'n' (common abbreviation eg NT for New Testament) and 'n' is found within the answer.
'partner' could be 'ally' (I've seen this in other clues) and 'ally' is found within the answer.
The remaining letters 'eer' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for eternally that I've seen before include "Nearly let out forever" , "Always and ever" , "For evermore" , "constantly" , "all the time" .)