My theory

I think the only thing I can come up with in the end as to why Edward didn't show up at the end is that he's still weak.

1. It can't be indifference. If writing the book had been cathartic and had helped him get through the abandonment, and he was now indifferent to her, he would not have sent her the book in the first place, much less dedicated it to her. If the reason he had not shown up at the end was indifference, he just would not have sent her the book.

2. If he'd forgiven her, he would have shown up to be the bigger person. Prove to her that she didn't affect him and he was moving on.

3. Revenge, ok, it wouldn't make him the greatest of characters, but not showing up actually robs him of revenge. I'd want to actually hear her say I was a great writer, I'd want her to beg me to get back together and then I would want to see her face when I rejected her. He couldn't do that. Why?

He's still a coward. He was too much of a pussy to show up and face her. That's really the only explanation I have. The end of the book did not prove him to be courageous enough to shoot the bad guys. He did accidentally and hurt himself more in the process. If Bobby is also part of himself, he's the part of him that wants him to be brave. His inner voice shouting at him to have courage.

In the end, Susan showing up and Edward not showing up prove that they are still the same people they were when they met. Edward is weak and she's still too concerned with money and appearances. Suddenly, Edward is good enough because he might have written one great book. Might she grow from this experience? There are hints that she might, like not firing that one woman.