Let her go and just be friends with her. You are too young and dispite everything she has done for you, like creepy said, don't put your world on the shoulders of one person who clearly is not strong enough to lift your world (she has her own heavy world to carry as well).
It's time for you to move on. Perhaps this is best for the both of you. Have you ever thought that maybe you are making her feel pain? Let go of your stubborn dependability and your fear of being alone (you have friends who are concerned about your welfare - you're thinking about cutting yourself and no matter how much you try to hide that pain people notice it, especially friends, not to mention your family) and move on with your life. Like my father used to always tell me, "do you "love" this person enough to want to marry them and spend the rest of your life with them?" (mind you he is very Christian, but in a good non-denominational way)
You will always love her because love cannot be broken through merely breaking up with someone. You should know this. Your mother passed this world but yet you still love her, and (in my belief system) she still loves you. Whats a mere breaking up with someone going to do to a bond that can even transcend death? (if you share my beliefs that is) When you two are ready, if you are ever ready, then join together again. If not, then ah well, you two will still talk and you will always remember how she lifted you up when you were in the pits of dispair after you mother died and never forget the bond you two shared for such a very very tiny part of your life.
Put down that knife, think about the good times anticipate that life is life and is not worth living without its bad times, and be happy. Hope my "baby" wisdom helps (I'm a youngling too, fresh out of my teens. Those dark years were truly "yesterday" for me)
