Clearly I screwed up the translation a bit here, lol. In the raws she says she "loves" her offhandedly as a joke in response to what Subaru said earlier. The second bubble is Subaru responding with a "bruh what" showing they're just joshin.
fuck me for thinking a manga was going to have a mature and sensible depiction of someone grappling with their sexuality, crazy how they ruined it in just 2 pages.
yeah this did strike me as rather odd, especially since Mark's father and Subaru both still call him Mark-kun. I guess she could still be grappling with the idea of honorifics in the same way Mark is that leads to his adorable "Subaru-chan-san".
I felt like this manga was setting up SO much drama and then it just ended? Understandable that it probably got axed but it did so little with the chapters it had that it was kind of inevitable.