Responses

I figured part of it out. When big bro told Shingo about why the scent disappears, he did not specify which person's feelings change only that "someone" had lost interest or grown unsure. Shingo immediately assumed it was Keichi's feelings that changed. ┗( T﹏T )┛
Keichi knows more about it than Shingo and realized that it meant that Shingo's feelings had changed, because Keichi still felt the same.
Kagami needs to get his shit together, like I don't even know why he blamed Shingo for the scent thing?? Do these people not know how their bodies work?