@DarkSlayer
Yes, he knew since at least chapter 128.
Chapter 128 page 16: https://mangadex.org/chapter/460459/16
Tarou to Ibusuki: "There's no point unless you can be happy as your normal self."
Chapter 129 page 5: https://mangadex.org/chapter/462728/5
Ibusuki: "Tarou... Getting him to know I'm a girl, that's enough for me..."
Chapter 130 page 11: https://mangadex.org/chapter/419551/11
Tarou: "Ibusuki-kun is a girl after all."