Maybe the mangaka was hoping for an ending that scintillates the reader's imagination, rather than spoon-feeds all the details. The whole story has had a bird-on-a-wire feel, touching here and there on important stuff, but not giving too much information to drag the story too deep into the drama. More like giving an overview so you get a sense of the main characters and what draws such opposites together and how they can fit together as they move into the future. This story to me feels like it's portraying the truly romantic side of life. Each comes with baggage, each varying personality types, but just enough in common to make a life together and to bring balance and harmony into each other's lives.
Following jalsy's comment here https://www.mangaupdates.com/series.html?id=55189
It seems like the author changed a lot in the story form the first published version. The ending in the first one seems to be different with the normal sex scene, so the story wasn't so open ended.