What events in "The Snows of Kilimanjaro" cause changes in Harry's character from beginning to end?

Harry is a bitter man at the beginning of the story.  He is harboring resentment towards his wife and wonders why he married her.  He is also dying from an infection in his leg (gangrene).  He begins to have flashbacks about his life, realizing that he will most likely die here in Africa.  As he has more flashbacks, his personality softens and he questions why he has so much resentment towards his wife and he realizes he has been too harsh with her.  At the end of the story, he is loaded into a helicopter (this is only an illusion, though) and the pilot heads towards the summit of Mt. Kilimanjaro instead of towards a hospital; however, in reality, this is his last illusion before he dies. His wife awakens and discovers him dead.  Harry, in the last hours of his life, has apparently had an epiphany of sorts and realized the errors of his ways.

How does Harry's attitude change throughout "The Snows of Kilimanjaro"?

Harry comes to understand that "writing equals life and not writing equals death" (Marc Seals). The time to write was over and now all the things he had held back (because he feared he did not know enough, or had other plans, or whatever interrupted the writing process) would never be written. Here is this realization at the end of the story, as Harry lays minutes from death:

No, he thought, when everything you do, you do too long, and do too late, you can't expect to find the people still there. The people all are gone. The party's over and you are with your hostess now.

Death is the hostess, of course. A rather grim party.