So you may notice the word “spoiler” above, which indicates that we are indeed going to divulge SPOILERS for Nocturnal Animals. You might want to read the spoiler-free review first. Or second? Who knows what you want to do, you loose cannon, you.
Here’s my evidence, and my theory, for what’s going on here, and what the ending means.
Susan and Edward were married. He used to call her a “Nocturnal Animal,” the name of the novel he sends her, and is dedicated to her. We find out that she loved his idealism, and wish to be a writer, and his belief in himself. Her mother tells her that she should not marry him, because he has no money. When Susan scoffs, her mother says “the things you love about him now, you’ll hate about him in a few years,” and that “everyone turns into her mother.”
We know by then that Susan has indeed dumped Edward, given up on her own dreams of being an artist in order to run a gallery of other people’s art, which by now she is bored with and feels nothing for. She is unhappy in her life, and her marriage, and her distant husband is cheating on her. So she gave up on Edward in order to pursue money, turning out just like her mother, and is now miserable.
She receives a novel from Edward [note she gets a paper cut upon opening it, tacky and obvious], and she imagines Edward as the main character as she reads [note we never see Edward alive in the present day]. His wife and daughter [both of whom have long ginger hair, like Susan] are killed. We find out that Susan aborted Edward’s child. We find out that Susan left Edward in an “awful, brutal” way. Susan was criticized for thinking Edward was weak, and the character in the novel is characterized as too weak to finish off the killer. When Susan is leaving him, Edward cautions that “she may never have this again.” In the novel, the main character dies alone in the desert.
Susan has walked by a prominent painting that says “Revenge,” and the ending of Edward’s novel is all about him getting revenge. Edward and Susan are to meet again for dinner, once she has finished his novel. It is never made explicit, but I came away with the feeling that he was dead by the end of the film [and there is a prominent dead bird, as well as a character with terminal cancer who is going to give up his short remaining life for “justice”]. We have indications that she is hoping to rekindle their relationship, because she wears a dress that is a bit more than friendly [above], and makes the decision to wipe off her lipstick as too forward. But she is stood up, and the movie ends with her waiting hours for him.
My theory is that his revenge is to make her realize how unhappy she is, and how badly she wants him back… only at a time where she can never possibly get him back.