[Grunch]

I fold becasue my gut tells me to.

Something a little more concrete?

He was either:
- slowplaying something the whole time (we win or chop)
- drawing & made it (we lose sometimes chop)
- blocking the river (we win)
- value betting the river (we lose)

#2 & #4 seem most likely to me, and since those are 'we lose' heavy, I fold.