50PLO Q5QAddcc: Should I be folding this river?

You can never fold the river. Folding the flop or turn you should be doing, but never the river if you've called 2 streets already. The decision you need to be making is typically on the turn.

Villain bet full pot on the flop, this is a huge indication that he at least has the ace of diamonds though it might not be suited. He has enough money behind him to bet almost full pot on the turn and river putting you in a terrible position even if he is bluffing.

Calling the turn bet was spew in my opinion. Fish typically don't bet without the nuts, so unless you thought he was a maniac rather than a fish I think the turn card is quite easy to fold to.

Most players are unbalanced on this turn card, they will bet less with weaker flushes, potentially taking a freecard as well but with a nut flush will pot it.

Fold the flop, sizing tells are huge in small stakes PLO, he will have you crushed like almost always.