Can someone explain the ending.

William Burroughs once stated that it was the accidental killing of his wife is what made it possible for him to become a writer. While he felt guilt about it for most of his life, it was also a liberating experience for him.

The land of "Annexia" in the last scene of the film represents the new world Burroughs has entered now that he has embraced his identity both as a writer and as a homosexual. The shooting death of his wife (and the memory thereof, which is why we see it twice in the movie) was his "ticket" into that world.