Interpretation- Every Character is a reflection of Susan
Susan is every Character in the story.
She is that which was taken away from from Tony. (Wife and Daughter)
She is the one that took it all away by leaving him and getting an abortion. (The Gang)
She is the weak one who could not see her own strength and fight for what she loves. (Tony)
She is the one who helped Tony realize he was weak and needed revenge. (Bobby)
And they're all dead. Just like Susan is now dead to him (No show).
That's why its called Nocturnal Animals. Because they all represent her.
Boom. Roasted. Movie solved. Everyone go home. We're done here.