Awww.
I mean, I kinda get it? Suddenly losing that something something "special" you shared with someone else because it was "special" to you.
But, I really hope Ootaki doesn't react too badly out of it besides just being jelly, cuz... WELL, Yakushimaru has to grow up and she wants to change... and even so, even if he feels a bit lonely about it... she also wants to be happy on her own, and he has to accept that too.