Is this a happy ending, or is it not? Actually, it's not really an ending. What is an happy ending in a life, anyway?
Now that I finished with the series, I really don't think it's YURI. It has, well, sex scenes, presence of which neither confirms nor invalidates YURI-ness of the manga, although it would tend to invalidate it for some people. YURI itself is not easy to define anyway, kind of like MOE is not easy to define.
But if this isn't YURI, what about "Ebisu-san to Hotei-san?" I consider that one YURI. So what's the difference? *shrug*