Is A Fold Possible Here

[theBruiser500]

3 handed, opponent is Svantekung, he seems to change gears between nitty and not nitty. Right now he is not nitty (preflop), but he doesn't seem to be betting much postflop unless he has it. However he's made a few big river continuation bets. I think one of them somewhere along the line has been a bluff (maybe this one).

I have 10k, he has me covered, he is in SB, and raises to 300, i raise to 900. He is calling most of my reraises. Flop is 7h 2d 8h, check check.

Turn is Ks, he check/calls my 1800, I think I succesfully made the timing on my bet suspiciousbut not sure. River is 3c, he leads out all in. It's hard to put him on a real hand with this action, at first I thought I'd have to call and win most of the time. But why his overbet? Then I started thinking maybe he has a big hand and is playing it real tricky. If the action doesn't make sense it generally works to believe the opponents river action as the truth.