Actually did you did you kiss Nox twice or did you take a bath when she told you too? Because when I kissed her twice and still supported her and not confronted her it gave me the banner that said I am getting the upperhand. i replayed and did the same thing and even confronted her and still got the upperhand. So I think it has to do with kissing her twice to begin with.
Yes, I kissed her twice when I went through it yesterday.
Actually, I just did a speedrun again (well, just loading a savepoint and ctrl fast skip through all the text, since this is just for checking lol).
First time I kissed Nox twice, gave her the cunnilingus at the bath and confronted her when the other Ravens abandoned the clan, following Katja.
This resulted in the "You're getting the upperhand in your relationship with Nox."
Now, for second try, I kissed her twice again, gave her the cunny, and agreed with her when the other Ravens abandoned the clan, following Katja.
This resulted in the "Nox is getting the upperhand in your relationship with her."
So in my save, it looks like confronting her about not doing anything about the other DR clan members leaving is the point where is decides it (storywise, it makes sense, given rest of clan leaving is a huge narrative point, compared to kissing, which is something minor).
Though I have no idea how you got upperhand in both scenario.