Nocturnal Animals (2016)
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Director Tom Ford has said in several interviews that it's up to the audience to decide why Edward stood Susan up. One theory (stated on the synopsis page in IMDB) is that he stood her up so that she'd feel the same emotional pain he did when she left him years before.
Edward may also feel he still loves her and it is too painful to see her again, or because she gave him the inspiration and strength that he needed to write his masterpiece and move on. Edit (Coming Soon)