the girl suddenly becoming hot, which seems more than likely to be what's going on here, is plausible enough. But it doesn't make for a very interesting story.

Especially since the girl is already ready to marry him. There's no obstacles whatsoever except for the completely artificial ones Harry creates using Ron and Voldemort. He doesn't have to win Ginny once he realizes he wants her now, after she's stopped wanting him. It's an incredibly smooth development of love that I always thought was maybe supposed to be a commentary about the way these things work. The way the girl develops this sort of thing young, but the boy isn't ready and is embarassed, and then she's again more mature and he's all awkward because he's caught up to her...