Youko is, in this chapter quite obviously arguing from a place of hurt. She got her lesbian awakening through reading class S togther with a senpai of hers who came onto her and then at some unspecified point must have gotten married to a man because she's holding a baby in the messenger app profile icon when Youko contacts her again at the end of the chapter.
Youko is in every way just mad that her first relationship didn't work out, probably in part because it was never defined as a relationship which lead her to want to define every "sisterly" relationship as merely the preamble to dating because of the way she was hurt by being in a a similar situationship rather than anything real.
So tldr; Youko is coping, she refuses to acknowledge any relationship that isn't explicitly romantic, because of the way her first relationship didn't define itself clearly, and it's still hurting her.