This is a fold imo. A hard fold, but a fold nonetheless.
A check-raise on the river after the way the hand played out like it did means he has the flush imo, no one bluffs rivers by check-raising (if he wanted to bluff the river he woulda just led out himself). Also a set isnt check-raising that turn, neither is a straight. Also if he had either he woulda led out on the river instead. Id expect him to have AX of diamonds here for the nut flush.

I would say he has flush here like 98% of the time. The other 2% accounts for misclicks and random min raise river bluffs.


Also I would lead out for a bit less on the river. $6 looks good.