Please help me...I cannot stop obsessing over her?

Every moment I think of her. Every thought, feeling, or action leads me back to her. Normal daily life has become impossible. I cannot even eat or sleep anymore. I am no creep, as I'm sure many of you will perceive me to be. She has a boyfriend who I have no intention of splitting from her... it wouldn't be fair to either of them. We are the only two people in the world that understand each other, she acknowledges this too. I don't feel good enough for her, though. She is beautiful, while I have no attractive features. I don't know how to continue life like this. I've tried distractions, hobbies, crafts... nothing at all can divert my mind. She is like the epitome of perfection to me. She is the girl I always dreamed of having, but never expected to find. Now I've found her, but I cannot have her. IT'S KILLING ME. It has nothing to do with lust or ... I just know that she is the only one who could make me truly happy... I have a therapist appointment this Wednesday, but even surviving until then seems impossible. This obsession has completely overthrown my mind, and I feel suicidal over her. I cannot tell her how I feel either; she is in one of my cles, and I that would be insanely awkward. She knows none of this, by the way, as far as I know.