That felt... strange. It feels like we're getting a peek inside the cracks of a relationship, without getting to see any sort of resolution by the end, even if the ending sounded hopeful somehow
People and relationships aren't always perfect. Even when there are cracks glaring straight at you, the resolution in this manga is an acknowledgement of Mei's faults and a reaffirmation of mutual love. It's the first step to a healthier relationship. Mei definitely needs to make it up to Yuiko with a bit more effort, but they do love each other a whole lot and are aware of it. The foundation's already strong so it's not that much of a stretch to think that they'll work it out somehow, but alas, we'll never know. Oneshots truly are such cruel pleasures.