This one would have been distinctly better as shounen-ai, perhaps? Their relationship-building, starting from people who don't get along to well, though to friends, is convincing. That being the basis for a budding romance kind of works, too, although it's only barely given enough time and reason to make sense...
But the more dirty developments felt a bit forced. And sort of seemed to advance the story in a fashion rather awkwardly perpendicular to the preceding plot and other bits of character development, somewhat to the story's detriment. Or so I felt. Obviously I'm being the picky one here, based on the other comments XD