I want to say something about this story, but I don't really know what to say as the experience was so ethereal...and I don't know how to capture my experience in words. But let me tell you things I know: 1. I really loved it. 2. It was so real...kind of heartbreaking but a lot more than that it was heartwarming, and somehow that heartwarmingness actually made it more painful...but in a good way. Gosh I'm sure it makes no sense at all. It's like trying to describe how a poem made you feel - it's too complex and maybe it really is not necessary to put it into words, (unless you are going to write a poem about it...). 3. My interpretation of your story is that Harry saw and knew, but after a frozen moment of shock his instinct took over and he went with pretending that nothing is wrong, except that he was not 100% pretending, because at the same time he had no doubts how much Severus loves him. Not to say he felt nothing about it, but he was able to choose what really matters. I like that interpretation better than that Harry had no clue. But even if he had no clue, I would like the story -- both ways are very touching but in different ways.
Finally, I sure don't feel any attraction to the concept of infidelity and would not normally want to read about that subject matter, but in this case it is not about the subject matter...I feel this is a beautiful piece of art...I truly, truly like it very much. I still feel...you know the feeling that a beautiful art gives you? The transportation to another plane, being moved, feeling something profound...is there a name for that experience? Well that's what this did to me.