Judging by what, apparently, gave her the final push, that is Nene saying that even if they got separated, her, Hotaru and Aoba are still good friends and are happy, I'd say Kou was not telling Rin because she is her oldest and closest friend.
If she doesn't know that Rin loves her romantically, she's most likely well aware that she is important to Rin and vice-versa. Then, perhaps, she knows it'll be hard on her and is afraid to tell her until the last moment. Not the right move, I'd say, but from the little we know, Kou is bit lacking in social interaction; not really sure about that, maybe I'm wrong.
last edited at Sep 13, 2017 7:21AM