* spoilers, ne? *
It was the only reasonable ending, really. When Natsuki (Yukiyo's "one true love") ends up staying with his parents for five days, he finally gets enough time with her to understand his feelings for her a little better. As he explains to his friend, it’s like holding a funeral for is former self.
After twelve episodes of thinking about whichever woman he wasn't with, in the final scene Yukiyo is still single, riding a woman's bicycle as fast as he can. But it’s not the sad ending you may assume. He's not the same insecure person he used to be, and his idea of his perfect love is shattered, replaced instead with a more realistic idea about the woman he's been moping about all this time. And once that has changed, he can move on.
It's a pretty philosophical end for a love story (well, three love stories, I suppose) and I’m happy that the writers ended it like this, rather than forcing him to pick one woman. Plus, despite his self-loathing, he ended up being a positive influence on the women he got involved with, so he's not quite the loser he says he is. And the last line is strangely uplifting and optimistic. I thought so, anyway.