I doubt that the most powerful Jedi ever is afraid of Sidious..
Now, I do believe that he is very much persuaded slowly towards
the darkside, by Sidious who plays into the mind of Anakin....
After years of persuation and working with his new mentor,
there is no reason to distrust him....
Vader has power and no rivals....
and then he finds his son, who poses a threat...
but a link to the past and a new powerful pair for
the future.....
Sidious, worst fears is for Vader to leave him
and join sides with Luke....
but he underestimates the power of bond
and father and son....
and is destroyed....
I don't believe Anakin fears the Emperor at first, as the Emperor continuously tells him he will one day be invincible. He just believes his guidance is best for Anakin's career. Once Anakin awakens as Vader, his old life will be meaningless. "That name no longer applies to me." Darth Vader will be all that is left, and nothing will stop him and the Empire from destroying the Jedi.
Anakin must have buried himself in the Darth Vader
persona as a way of shielding himself from his deeds and decisions.
When faced with Luke, he can't deny his past any longer....
I kind of like the theory of Anakin being dependent on Palpatine in the OT.
Destroying the Emperor meant killing himself but it was worth his son's life...
The way I see it, Vader is too set in his ways to change. His line in ROTJ to Luke: "It is too late for me, my son" implies this. He knows he's a great evil, and that somewhere inside of him Anakin Skywalker is raging against the darkside. But it's no different than the junkie who knows that doing drugs is killing him, but continues to do them. Anakin has a problem...
i see it as guilt and self hatred....i'm happy with that, i understand now why he turns completely to the dark, why he refuses to acknowledge his previous persona, and have some sympathy with the character in the ot....the whole saga makes more sense to me now....one of my favourite bits of writing in the prequels so far....