And here come the Intrusive Thoughts. Always the worst when they get you late into the night, in the comfort of your bedroom, after an emotionally exhausting day. That said, I get why she has these doubts, and they’re not entirely unfounded given her perception of Kanon up to this point. Some of that is even Kanon’s fault for how she chose to tease Saki early into their relationship, something the former did acknowledge shortly after her big gay epiphany.
Of course, Kanon has changed a lot since then, but it’s been a gradual change. Saki, who has spent nearly every school day, and several weekends, practically attached to Kanon‘s hip would hardly notice it, or attribute any change in behaviour to her just coming out of her shell. And while yes, she has, people outside their relationship, especially their classmates, can see that Kanon acts differently when Saki is or isn’t around. It’s the same with the photos, Saki didn‘t have a particular reaction to them because to her that’s just how Kanon always acts around her the past few weeks, nothing noteworthy. She was probably more relieved that her own face was slightly less expressive as it meant her own feelings probably weren’t showing as much.
Also, as someone mentioned before, Kanon has felt the first sparks of an emotion she couldn’t identify back during the summer fireworks, and has been interrogating her feelings towards Saki since. However, as far as I can recall, the only person she ever told about that specifically was Miura-sensei. Saki had no idea that Kanon spent weeks or months trying to figure out how she feels about her. That‘s another reason why it feels sudden to her.