Occam’s Razor
Take it as you wish yet logic or simplest explanation are not really terms which can be applied to Citrus. I have never heard of 2 people who love each other to be able to sleep in the same bed for 1-2 years without some physicality happening.
In fact in ch 4-13 Yuzu while going to bed was saying “be quiet my heart Mei will hear” “I want to touch her hair her skin even with just my fingertips” and on slide 14-15 she was literally on top of Mei grinning. Fast forward to today and Sabu is trying to rationalize romance (which is a fallacy because there either is or isnt) by saying “before marriage there is dating and we’ve only just started" "I should properly go through the steps from the beginning" whereas a much more down to earth Matsuri responds "but she's already proposed to you , so why now..." Go ahead and find Occam's Razor in that.
https://dynasty-scans.com/chapters/citrus_june_2nd#17
You’ve done a good job of pointing out Saburouta’s deficiencies as a long-term serial storyteller. From my point of view, she’s basically rebooted Mei’s character several different times, and while I can speculate about her reasons for doing so, it would only be speculation without any real evidence.
The fact that she’s had characters (mostly Matsuri, but also others) point out the counter-intuitive developments shows that the author is aware of them, but I suspect she believes that Hanging a Lampshade on such problems makes them simply go away.
https://tvtropes.org/pmwiki/pmwiki.php/Main/LampshadeHanging
As with some other series with intriguing premises but muddled writing and plotting, readers have made a cottage industry of patching the logical and narrative gaps in the story and characterizations with complex theories and headcanon.
It’s even possible that Citrus might have been a more interesting series, and one with more consistent characterizations, if Mei had been conceived of as victim of sexual abuse from the beginning and that idea developed throughout, or if Mei had actually been engaging in sexual liaisons behind Yuzu’s back. There’s simply no convincing evidence in the text itself that either of those things is the case.