Infatuated best man holding ring (8)
I believe the answer is:
besotted
'infatuated' is the definition.
(I've seen this before)
'best man holding ring' is the wordplay.
'man' becomes 'ted' (Ted is a man's name).
'holding' is an insertion indicator.
'ring' becomes 'o' (letter resembling a ring).
'best'+'ted'='bestted'
'bestted' enclosing 'o' is 'BESOTTED'.
(Other definitions for besotted that I've seen before include "Smitten" , "Foolishly infatuated" , "Doting" , "Bested to become infatuated" , "Strongly infatuated" .)