Sayonara, Heron
Two high school friends become sex friends, semi-permanent roommates, and then, maybe, lovers. Mostly an investigation into the boundaries we draw between ourselves and others in our life, and how much we need to negotiate those boundaries when we strive for intimacy or a deeper relationship (cue Kate Bush -- "Hello, I know that you're unhappy / I bring you love and deeper understanding"). The main characters don't fall into a traditional romance even at the end, when they reach an understanding about their feelings, and there's a wonderful scene where one of the characters confesses that the phrase "I love you" is too much for him, because he really doesn't understand what it means yet. Realistic, slow, and not much happens except for the central conflict (which is resolved, primarily, off-screen), but sweeter because of that, because you're truly cheerleading for the success of the relationship even after you turn the last page.
Hidamari ga Kikoeru