The problem with all of this romance is All of This Romance. It dominates the movie, drawing our focus away not only from major plot points – which fall disastrously through the cracks – but also deters the mood, which, in a (nearly) penultimate film, should be at the forefront.
The title of this film is Harry Potter and the HALF-BLOOD PRINCE but the title character gets next to no screen time and even less explanation, save for a few asides that, if you haven't read the book, may as well have been cut. Better to call the movie Harry Potter and the Hormones from Hedes and save us our disillusionment.