Amorous actor in plays about marriage, primarily (8)
I believe the answer is:
romantic
'amorous' is the definition.
(I've seen this before)
'actor in plays about marriage primarily' is the wordplay.
'plays' indicates an anagram.
'about' indicates putting letters inside.
'primarily' says to take the initial letters.
The first letter of 'marriage' is 'm'.
'actor'+'in'='actorin'
'actorin' is an anagram of 'roantic'.
'roantic' placed around 'm' is 'ROMANTIC'.
(Other definitions for romantic that I've seen before include "Amorous, showing loving feeling" , "Passionate" , "Coin mart (anag.)" , "Relating to love" , "Soulful or amorous idealist" .)