I understand the book at last

Rating: 10/10 (6 December 2019)

So I read the book, and have to say the film is 100% faithful to it, absolutely perfect. But, after finishing the book I had lots of doubts about what exactly happened, I didn't really understand the ending. Now, after watching the movie it became crystal clear.
Teddy was really Andrew Laeddis, and in the scene almost at the end (2:04:00) where he wakes up from the fainting, he really accepts that he is Laeddis and Dr. Cawley wants to help him, but he has no thoughts yet about the lobotomy. However, a few days later in the next scene he is still his real self as Laeddis, but he is already afraid that he will regress again as he always did before. Therefore when talking to Dr. Sheenan and he already decides that he wants to get healed for good and also accepts possible death ("What should be worse? To live as a monster, or die as a good man?"), therefore he pretends to have regressed so that they perform the lobotomy on him - Dr. Sheenan buys this, calls him Teddy after he signals to Dr. Cawley that the lobotomy already is inevitable.