Originally Posted by Nancy Allen``
Sold Vader out? The only way I think the Emperor may have done that is by trying to kill Luke, which Vader didn't want. Is that what you are referring to?
Before Vader brings Luke to Palpatnie, they converse slightly on Endore. What is intresting, Vader sounds like he knows he is going to die.
At the beginning of their battle on the Death Star, Vader stopped Luke from killing Palpatine due to the fact he was defending Palpitine.
When Palpitine say, "Kill your father, and take his place by my side." was the defining moment, which Vader realized his master was truely out to finish him.
Vader tried to pusuade Luke earlier to kill Palpatine, and to fight along side him to rule the galaxy. In essence, Vader was going to betray Palpatine in the first place. However, Luke convinced his father that he was still a Jedi, but he needed Palpatine to tip his set of cards.