I hope after this she will realise how stupid she of for actually thinking about breaking up, just because 'shE wOuLD bE hApPiEr witHoUT SomeONe lIke ME".
Spoiler for those who want to know what the next chapter is about:
It's just how these two met. And it's a very short one, so the next chapters will still be about it. Also, her friend seems to be totally serious.
Jokes aside, I'm 90% sure she's just kidding, cause that came outta nowhere. She's probably just gonna say something like "see? You don't wanna leave Kaori, so why are you entertaining those thoughts in the first place?".
But any way you look at it, there's no chance of Kayoko leaving Kaori, so there's literally nothing to worry about even if she's serious.
EDIT: also, the author just posted a cute Halloween comic of Kayoko and Kaori on twitter (I **think** it's just an extra, though the text in Japanese might contain spoilers from later chapters, idk): https://twitter.com/_osakana_man/status/1322955936676261894