The Marriage tag is too broad, to the point where it's hard to really use it to find things. It's currently used for proposals, weddings and pictures where characters are wearing wedding rings.
I suggest at least making Proposal its own tag.
Virgin's Empire has been going since 2010 and only about a year has passed in their time. Must be the immense density of Ayano and Miyoshi causing a distortion in the fabric of spacetime.
That's just the time warping effect of slice-of-life and cute girls doing cute things. Yotsubato! has been going on since 2003 and I think it's been like less than 6 months in universe.
I'm not sure it's what your looking for, but it reminds me of Raubritter. Two cousins that help solve mysteries for women, with a police officer at the end.
Actually, that's exactly the one I was thinking of! Thank you. It's been so long since I read it that the details got a bit shuffled in my memory.