One small raise in MP to 15, one call SB, who's a total donk with 400 and I call with [8c] in the BB.

Flop [4c][5c] (45)
Checked around. Smart letting the others bet, on my part.

Turn (45)
Checked to me, I bet 32, MP calls, now SB wakes up and bets 70. I cnly call. MP folds.

River (215)
SB pushes for his last 315.
I have a straight flush, and I also have the nut flush, i.e. I have the 2nd and 3rd nuts. Is there any chance that he doesnt have the nut