You are not providing enough information. All we know is cards. It is not clear if you had position. What is huge bet on river?
On the flop you have nothing but Ace high and a gut shot straight draw. There is no reason to build a pot here. Your Ace has some show down value. If you call the flush cards dead you only have 5 outs (3 3s and 2 Aces).
If villain got in late and for a good price that flop is in their range. If villain was BB he got in for 3:1. If villain is on a flush draw they have more outs. Since any pair is an out they are on 15 outs. If you try and price them out then you have priced yourself out.
Be happy villain checked the flop. You did not improve on turn. 8 could have hit the villain. Be glad villain checked.
You got the worse possible river. A bet of 2.5X the pot is nuts or a stone cold bluff. Would they play flush draw that way - the answer is yes. Just release. At this point you are only out 4 BB. It would need to be 5/12 chance that is bluff to even break even calling. Only a maniacs bluff that much.
If you were out of position you could have led out for 1/2 the pot to look like a flush value bet. If he comes back then you are pretty sure he has the flush. But in the case you could be pretty sure he had it without investing another 1/2 pot.
Why did you even call 4BB from mid preflop with A5o?