What a twist!

The way I see it, the ending of the book conveys the message that sometimes a rash decision can precipitate a series of chaotic events that are ultimately irreversible. "So for instance, if Tony..." had been different, had never sent the letter, and was more careful about how he affected others, perhaps what happened would never have occurred. 

When the reality of Veronica's situation is finally revealed, one can see that it was quite possible that Tony's letter prompted Adrian's suicide. Perhaps, even, it sent Adrian into the lion's den with the comment urging Adrian to consult Veronica's mother.

Since the novel is written from Tony's point of view, and in a steam-of-consciousness style, the reader can experience the shock, horror and remorse that comes from inadvertently ruining someone's life. When we first hear about the letter Tony sent to Adrian, it is only in passing. Very little is described, so when the reader is shown the letter Part II, he/she is ultimately as shocked as Tony is. 

Tony did not curse Adrian and Veronica, but he may well have played a main role in their misfortune. His actions, however accidental, are irreversible. The knowledge of the consequences of that letter will most certainly haunt him for the rest of his life.

Adrian, whom he once regarded as a sort of martyr taking control of his life, was no different from Robson. He was afraid, lost, and confused. Suicide was not a noble act; it was an escape. His last letter was an excuse, not a reason. Everything Tony thought he understood has been completely turned around, and he is left empty, alone, and full of remorse. The 'closed circle' he was searching for can never be mended, and he will never achieve the "sense of an ending" he so desperately craves. 

This novel was like no other I have ever read. The end is haunting and sharp. I was left with the feeling that nothing in life is certain, and that oftentimes, we affect each other in ways we never imagined possible. It is a powerful commentary on modern-day society and human interaction.