He had always known what it meant to be a hikari - that above all else, you side with your darkness. That above all else, -your- darkness is right, no one else's.
After all, how could the other half of your soul be wrong?
So when Bakura decided one day that they needed Domino, it was nothing at all for Ryou to pack his bags, and they left.
And when Bakura decided that the girl that Ryou liked needed to die, well....it wasn't his place to question.
And then Bakura decided that he loved Ryou, and that they needed to stay together for eternity...well...
Ryou didn't have to question.
He knew that Bakura was right.
As he always would be.