Most shipping fics for Harry Potter during his school years have believability issues because they transcribe the concept of teens in love very poorly.
Here, though, we learn why this is not necessarily a bad thing. This is a very good, very well-written story with a slight problem about telling rather the showing. But if Harry and Cho are in the same place, particularly if they're near each other, it degrades badly. It does this because, well, they're teens in love, and the author has managed to perfectly capture everything about a relationship between people of such an age that's painful and frustrating, and preserve its essence. The avoidance, the passivity, the awkwardness, everything else about them that will be chewing up your time and your patience, it's all right there on the page, and the reader is subjected to it all.
Other parts of the story are interesting, even fascinating, in their own right, but the thing that got this recommendation put in this section is the story's worst point.