lol. you folded the best hand, he made a worse flush.
no 25nl reg is checking back a boat OTT. and i hate reading shit about 'yeah, ofc he checks back a boat, cos he knows youre on a draw and he wants you to catch up'. stfu, that is stupid. if he knows youre on a draw, then he should be making a small bet OTT, around or slightly under half pot, so that he induces calls from draws and continues to build a bigger pot with his nut hand. anyone who checks back a boat on this turn is an idiot, and might i add that multitabling regs are much more likely to fastplay, because a) you get more value, and b) you dont have the capacity to play non ABC while playing a ton of tables.
bet/call or bet/raise flop, bet/fold turn unimproved. and yeah as played, you have to call off river.
i also think that if you check the flop, you should be doing it with the intention to c/r, ainec