see the thing is that when he "jumps" at Luke and says "that name no longer has any meaning to me" hes doing it in a sort of emotional self defence. vader is not the hardened sith that we think he is. he regrets his past, he basically makes a deal with the devil and has to live his life with that deal which haunts him day and night. no one. not even a sith could live with all that inside him for that long without releasing something. you can tell that vader does still have that emotion and regret when Luke says "then my father is truly dead" and vader goes to the railing and is obviously in conflict. maybe ur right, maybe vader doesn't want to go back because he wants to forget his past. but i dont think that it fits the whole thing that is vader. the point is hes suffering, for like almost 20 years. "fear leads to anger, anger leads to hate, hate leads to suffering" (a good connection to anakin's future in TPM) i dont think he has forgotten. i think he remembers completely and it continually drives him to anger and that turns into more pain. thats what makes vader so interesting and why ROTS is going to be so good, cause we will realise what vader did, and what he had to live with.