Every group of friends has that one bitter person who can't just be happy for their friends whenever they get a significant other and so either complains to everyone and/or impose themselves onto any and all possible romantic outings without getting into an actual relationship of their own.
Seriously, Kisaki is giving off some incel vibes here (or femcel if you want to be pedantic). It would be one thing if she was just sad over being single, then I would sympathize with her somewhat, but it's an entirely different thing to act petty towards her friends and their respective boyfriends. How is this kind of character supposed to be charming or likeable?