Yup, this is a special one!! First of all, vers couple. Second of all THE STORY OMG. The HONESTY of the confessions! And the translation is fantasic, so natural (almost *too* colloquial at times), they feel like just a couple of people who happened to meet.
And then on top of that, all the sex is for a purpose that advances the story a bit (while also being really good)
Sayonara Okaeri Itoshisa ni -Koi ni Tsuite, Oshietekurenai ka-