I feel the criticisms of the series as a whole, and of Yagi as a complete idiot are very unfair. First of all, in the original story, you see them appear to be about to kiss, but it's kept ambiguous as to whether they do and whether they are a couple. This sequel resolves that ambiguity and reveals they did not and are not; that's all there is to it. With that in mind, Yagi's behavior is understandable. She clearly likes Mado, but can't accept that Mado likes her back due to poor self esteem, so she decides to give another girl a chance. I've seen several of my friends in real life do this, it's not always a bad or stupid idea to date someone who's really into you when you already have a crush. Personally, while I'm eager to see Yagi and Mado end up together, I don't see every obstacle along the way as a writing flaw.