Why Did Roberta Do This?
First, let me say that I know the real answer to this question is that it was not time for the movie to end yet; however, here is a major plot hole I don't understand.
Roberta has regained her memory and slept with Dez as Roberta, not as Susan. They wake up the next morning and are about to resume making love when Jim comes in.
Dez and Jim argue as Dez admits to sleeping with the woman he still believes to be Susan.
Roberta is feeling all guilt ridden and full of stress and leaves without even saying good bye.
Why?
Was she hurt that Dez told Jim that sleeping with Susan (her) was a sh**tty thing to do?
Was she feeling guilty about having cheated on Gary?
She had regained her memory. All she had to do was come out of the kitchen. When Jim saw her, he would know Dez had not slept with Susan and the argument between the friends would have been over.
Was Roberta just depressed to be Robera again instead of Susan and let down that a night of great sex with Dez did not solve all of her emotional problems?
Why did Roberta leave and not just come out of the kitchen when Dez called to her?
The way that she left, you got the impression that she was through with Dez, but then she went back to him at the end.