While watching Savages (2012), I couldn't figure out if Ben and Chon both knew about each other sleeping with O. I'm suspecting that Chon knew about Ben since I believe they explained it as O was his girl?
Did they know they were sharing her?
I haven't made it through the movie, but in Don Winslow's original novel (on which the movie is closely based), Ben and Chon are both fully aware and accepting of the fact that she sleeps with both of them, regarding O as the bond that holds them all together.
The book's a great read. Amazon link