Plot Theory

Since I haven't seen anyone bring this up then I assume Im the only one standing by this theory. I took the ending as a reveal that John actually had split personality and was Mike as well. That he had come to Gertles house before and did terrible things to her, and thats whys why she was so welcoming to him to come into her home the second time. That also explains why she was relieved that he told her that he "killed Mike" and therefore killed the evil side of himself. But in the end, out of fear of Mike coming back, she had to kill him.

I know that there really isn't too much evidence supporting this theory and really its just a personal assumption but I thought that this twist tightly rapped up the plot. Anyone agree?