I feel very bad for you...really. But I do agree with GYMGIRL...there was something lacking, something within her that you could just not solve. No matter what you could say or do, you have to remember that it is not you it's her. You sound like an amazing BF who did all he could to keep it going, but sometimes no matter what you do it's never enough.
Keep your head up and in time it will pass. You will never forget her or the relationship, that is a given, but you will find someone else eventually. The next person may be even better than what you had before. Best wishes!