Hey now... I don't believe it.

I noticed her nickname "Yashiko" comes from "Hayashi Kotoyo"...

I wonder if she's still with the teacher

So Yashiko either dyed her after that story or she stopped dying her hair black after said story.

Honestly, Tsubomi sounds kind of manipulative. Her heart is in the right place, but her actions towards Ayumu aren't healthy.