From the first chapters, the breast wasn't "fated" for the heroine. He was first used to harass her, and only became her companion after the defeat of the "villainess".
This chapter is turning things bad.
Also, it's another one of these "heroine" who is also reincarnated and takes her "destiny" for granted. I don't necessarily mind, but I'm not a fan of "compelled events", particularly after the mc managed to change so many things.