I'm not asking about original authorial intent. What did you take away from the book as the most important point?

For me, it was about how dwelling on the past and loss from the past, whether as nostalgia or as depression, is useless. We don't WANT the situation to return, because if it did it would already not be the same as it was - you can't step into the same river twice. We have to let go and move on. Kris was very sad about losing Harey. He blamed himself for her death. He lived with the pain and the feeling of loss. At the same time, the relationship was very dysfunctional from everything mentioned in the book about it (including, if I remember correctly, the age issues). Harey was obviously co-dependent and unstable, and ultimately she's the one who killed herself. Kris didn't actually murder her.

The whole experience of having her come back allows him to re-assess the relationship. He remembers why he needed to leave. He remembers the things that the passage of time had made fuzzy. He realizes that, after so much time, he can't remember the whole relationship and that he has been selectively remembering those things that he chose to remember for his own reasons. He ultimately lets go of Harey. It allows him to move forward.