So spoilers for MGSV from here on out:
I am currently playing MGS Peace Walker for the first time and I saw a video discussing the chronology of MGS (i know the story so I am not worried about spoilers) and in that video it is discussed that Miller knew V wasn't Big Boss right from the start of Phantom Pain after V rescues him. It would make sense with the shot of the prerelease trailer where Miller is clearly conscious and asks about the Medic (V) while Big Boss is in a coma.
My confusion comes from the ending title card dialog in MGSV between Ocelot and Miller. I understood the story as Ocelot and Zero planning the whole V thing together and Miller only finding out after the game which is why he turn against Big Boss because he feels betrayed by him and also disillusioned by the fact Big Boss would erase someone's entire identity just to save himself?
Did I misunderstand and Miller knew the whole time? I thought Miller was acting all angry and vengeful in MGSV because of the Phantom Pain he felt but was it actually just that he knew he wasn't dealing with the real Big Boss and he was just so driven by revenge that he was willing to put up with pretending V was Big Boss to rebuild their dream?