What does the ending of Nocturnal Animals mean?

SPOILERS AHEAD

I think this movie is actually about revenge.

The whole movie is based on two "parallel" stories. The events in real life are very similar to those of the book.

One is the relationship between Susan (Amy Adams) and Edward (Jake Gyllenhaal) a.k.a. real life where she reads the book. In this (lets say) universe she cheats on him and breaks his heart. At that point she is also pregnant with Edward's child (which we see at some point in the movie when Susan calls her). So basically, he loses them both.

The other story is where Tony's (also Jake Gyllenhaal) wife and daughter are killed in the night they where driving through nowhere.

Do you see how these stories are now similar? In both, Edward/Tony loses his wife and daughter.

Now in the book he seeks revenge for what happened to his loved ones and actually gets it. One guy is killed by Bobby (Michael Shannon) and the other Tony kills himself. On the other hand, in real life he gets his revenge by not showing up at the restaurant. He knows that the book would blow Susan's mind and bring back the feelings she had for him in the past. She also told him at some point that she doesn't think that he should write about himself in his books. But that's exactly what he did and he succeeded.

So in the end I think this is exactly what she realizes.

P.S. Another huge clue that made me come up with this theory is when Susan is at her art gallery. She pauses to look at the huge painting saying 'Revenge' and saying that she couldn't remember where did it come from.

The message that I got from the movie is that Edward was a great writer without having to go though what she wanted him to do in order to stay with him. In the end he was brilliant and successful and she was married to the "successful" man who wound up being the two timing broke guy who is leaching off of her success. He stood her up in the end of the movie to remind her that love was supposed to conquer all and she gave up on him when he needed her the most. He wanted her to read how great of a writer he was and in the end didn't want to have anything to do with her anymore.

His objective is clear. He wanted to show her, through the parallel story, the pain he went through when she left him and on top of that aborted his child.

Ultimately, he didn't show up to make her aware that she's not worth and that he had his revenge on her.

After reading the book, Susan admires Edward for his work and agrees to meet up at a fancy restaurant. She dresses beautifully and looks happy. Maybe she wants to patch things up with him or maybe she decides to live with him for the rest of her life. She looks determined. However, after hours of waiting, Edward doesn't show up. She later realizes that the book was an analogy to prove his life with the book in the sense that Susan killed his wife and daughter so he's already dead by not showing up. Further, Edward knows her emptiness. She wasn't there when he was in intense need of her. And he decides not to be there when things were going not well for her. It was a sweet revenge.

The ending also proves Edward is over Susan and he is no week anymore. He is living 19 years without her and can live rest of life without Susan.

As there are a lot of theories regarding the movie ending, the only person who can answer correctly is the director himself. The story itself is not open-ended and needs a lot of assumptions.

I have also written a brief about the movie twist here: http://prabinparajuli.com.np/noctural-animals-movie-plot-ending-twist/

In the end, it's clear. Tony uses what he KNOWS is going to be a best seller, possibly a Nobel or Pulitzer Prize novel to seduce her. To show her he always had it in him to be a great author without having to compromise his integrity. She, on the other hand compromised everything, only to have an empty and superficial life which she swore she'd never do.

He knows now that he's a great writer - she'd come to him asap, when before she wouldn't spit on him if he was on fire! Sure enough, he sends her 1 text inviting her to meet with him and she jumped at the chance! He's outside the restaurant watching her having a drink while she's waiting. He never goes in. The meeting was to show her she is STILL superficial and miserable - while also proving you can have integrity and class and still be successful.

From the book, when Tony has the redneck psychopath at gunpoint he still can't do the right thing, he ended up dying. His senstivity became his weakness.

In the real life, Edward stood up Susan because it's the right thing to do, he didn't let his sensitivity get the best of him and try to go back with Susan bacause that would probbably kill him too like how Tony died. It's pretty poetic.