On the river the villain is making a defensive bet to name his price for the showdown. He has a strong hand and is scared you are going to bluff more than he is comfortable calling, and is also pretty sure you have the flush. I'm not shoving over the top but I don't think the villain can help but call a small raise here.

Is this the kind of opponent you think is going to come back over the top with a bluff? If he comes back over the top you are beat and it's an easy fold. You are two scared of a flush imo. I can't see a flush betting less than 1/3 pot on the river.