Him wanting Luke by his side, which I never said he didn't, doesn't show him as conflicted. Vader asks Luke to join him so he can complete his training, telling him that he doesn't know the power of the Dark Side, and that he can destroy the Emperor so they can rule as father and son. There's no light/dark conflict involved in the proposition. He's trying to turn Luke.
We know that Vader had the light/dark conflict going on because Luke told us so, and then Vader proves him right by killing the Emperor, not for his own gain, but to protect someone else. Before that moment of him turning on the Emperor, everything Vader does is consistent with someone dedicated to the Dark Side.