Oh, I'm so glad to see someone else who had the same kind of reaction I did! I feel so strange about how I've reacted to this story, and it's hard to articulate just what *bothers* me so much, but your mention of how you 'kept cringing waiting for the big scene where they break up' and then how the ending--sans said big scene--'makes [you] worry that it will happen again,'] strikes such a chord. I think that may be the central issue for me. It's such a well-done story, so lucid and articulate, so careful in its detail, so *persuasive*, you know? I can see such infidelity happening just this way, and I think even more than the constant low-level background tension of 'will Harry find out in the course of the story' or 'will it happen again' is 'will Harry find out some time in the future?' if that makes any sense. It casts a pall over the entire imagined future, if that makes any sense.
Agh! Enough obsessing over this. I still have a bunch of stories to read/comment on by Sunday!