Soooo many rom-coms have done this lately. Start a really interesting concept and then just drop the premise and go regular shoujo manga. Like, here's the backstory and reason this will be interesting and could cause conflict. Got it? Good, because we'll never bring it up again after chapter 3 and this is gonna actually be a regular boring rom com with all the tropes.The author better not have an idiotic reason for her to turn down his proposal OR forget about it ALL TOGETHER
I think more likely one of the twins died and the surviving twin never talks about her.No wonder she said no, he's stupid and probably only cares about himself, considering they got that far and he never even knew she had a twin.