You guys ruined it, but: Mei is such a normie. She just gets the basics wrong and doesn't pay enough attention to her lover. In which case, why have a lover? If you're not emphatically into your lover above all else...but then she's had this work load since she was placed in her grandfather's shell.
This manga is actually about seniors raising kids and what that looks like. Looks bad, but I think in this case Mei is the casualty of conservative traditional old-school thinking. And in ways that's a comment on Japanese society since it's politically run through the above-50 set. They have all the power and basically are Japan, it's why they only got rid of bureaucratic seals recently during COVID.
Sly Saburouta politics? Mei's also in the ultra-wealthy class as well so she's a comment on the top .1% as well. It's funny how it's a poor vs rich relationship. And it's funny how they're quibbling about birthdays when all we wanted was some more of that summer H E A T S T E A M from before chap 36.
My advice is to not keep your pants on or wait and prove your love once and for all.