Earth calling Kanoko...how much longer are you going to give Sumika hope? Can you please tell Hime that you like her, or rather that you used to like her, because at this point you no longer want Hime as a partner; you've already changed your target. All that's left is for you to have the courage to reveal to Hime that you once loved her, and as you said, you've already found someone else who loves you and who you love.
She did. During their date, after the incident with Goeido, Kanoko tells Sumika that she wants to continue being her girlfriend and even in the weeks before then it was clear Kanoko was committed to giving herself to Sumika. (Albeit to an arguably self-destructive degree.)
It was Sumika who refused and broke up with her, insisting Kanoko has to confess to Hime first. And Sumika is probably not going to accept a confession until she does. So now Kanoko is in an awkward situation where she can't go out with the girl she wants to until she "confesses" to the girl she gave up on. A girl who last time she was confessed to almost broke off all contact with Yano. (Which ironically Kanoko helped put back together.) And if that wasn't emtionally taxing enough for a teenager, this condition was dumped on Kanoko right after she got SA'd.
Honestly I think Sumika's meddling is the hold up here. I know Kanoko needs closure but Kanoko stopped trying to talk about Hime with her a long time ago now and its clear she'd be a committed gf.