The thing is, since he just called on the flop and turn I figured he had a draw without the ace. Would expect tp+nutflushdraw to raise on that flop, so I was expecting some random J2 sooted. Of course, seeing the flush completing on the river I checked. When he bet I instantly got the idea that "hey, maybe he is just betting because I checked", the fear of being bluffed make me do bad calls sometimes.