You do understand that you're reaching, right? You're making huge leaps to explain why Kat would be affected by the MC's secret plans for SR. I get it, and you may well be right, but at the moment I prefer small steps: Kat couldn't possibly know, SR's shown no signs of sexual jealousy (yes, murderous rage, but not over this, and the MC has had sex with Kat since they started accumulating affection points). Kat hasn't shied from all the MC's demon actions. SR hasn't stopped the MC from doing anything with the team. Nothing in the actual text of the story suggests either condition has changed. If it has, and it's impossible for the player to know, that's pulling the rug out from under the player without any possibility of warning, which would suck.
I keep asking: why? If the love route's still open, why isn't the scene? Give me a reason based on the story thus far, not an assumption about where it's going.
If your answer is "because it's problematic to get too close to a demon," that's fine, but that's based on an extrapolation. It might be, but there are no cautions or warnings in the current text. And even if there were, they'd apply just as much to the MC, yet Kat (and, presumably, the others) haven't yet cared.
I think now you're just trolling me. I please ask other readers to tell me if my explanations are that dense, as you keep asking me why Kat would be affected by the SR situation and unwilling to see MC. Which is something I never said nor use as a justification. I'm saying in all my posts that Kat is not the problem, she's not who prevents you to go back to her because you are too close to SR.
It's a forced choice made by the MC himself because A)he has nothing to report to the team (and this a fact, not 'reaching',
as in every other path he learns from Vord how to kill SR and quickly goes to let his team know about the last part of the plan, and only then a sex scene happens), and B)kissing SR is an obvious milestone on your relationship with her (doesn't matter if your intentions are real or fake, the milestone is there and SHE thinks is real), so leaving her after this (no matter for what, but just for having sex with other girl seems especially unwise) could be seen as an unnecessary risk of being caught on your hypothethical betrayal. And yeah, reason B) may be 'reaching' as you put it, but it's not as unreasonable as you seem to think. Although I guess you'd ask for a line of text in which the MC explains literally this. Yeah, unfortunately that line is not there.
About your 'nothing in the actual text of the story suggest either condition has changed', well I see
Vord's words about him trying to confess his love to SR back in his times, then SR's story of being punished for not understanding what was The Great Other's vision for her, then the MC trying to win her over to be her key to find peace at last, then the kiss, and finally those lines I already mentioned in which SR tells MC he was right (literally the end of the chapter in SR's perfect path). it's now, after that last speech before entering the cave, when she finally changes the way he sees the MC, when she accepts all his flirtation and opens up to him because he says the things she was already starting to think: that he's the plan her god has for her. She (SR) has changed, it's obvious. As in every other game with a score, it's not the first affection point that made her change, but the 6 combined, the last one being the definitive trigger.
So again, I don't think I'm 'reaching' that far when I say SR wouldn't be happy if you keep playing the field from then on. Don't you think she would have asked for the first time 'where had you gone after kissing me', especially now that you control your demon form and can travel wherever you actually wants? Don't you think it's reasonable even for a treacherous MC to stay low for a bit before being totally sure he has subdued SR? You have closed your trap over her, why risk it by flying away from her. The love routes not being closed suggest that us players will still be able to choose if our plans for SR are made of real love or if we are just trying to defeat her without killing her and then ride into the sunset with our wife. But, again, that was not the moment to go and fuck around.
If you don't give her that last speech, if you don't push her to reflect on her actual feelings and fears, she just keeps going with her plan and doesn't give a shit about you disappearing again. Depending on your affection choices she might think you're not opposing her or she might suspect you're doing something shady, but in the end she's never interested in your sexual adventures. After basically telling her you love her and she should love you, though, it's kind of natural to think this has changed.