With the flush draw on the board, I don't think you have the odds to chase the dummy end of the straight here. What do you do if the river is the 5 of spades and he moves in on you? do you still call?

As played you have to call the river as a donkey two pair might show up. In an unraised pot with this many players drawing to the small straight with a flush draw and higher straights on board can create some difficult decisions...