Oh sweetie..I don't have any great words of wisdom for you, I'm just not that qualified, but I can listen.
The only thing I know for sure is that you are so young.(i read your profile), and, believe me, I know that means nothing to you at the moment, but your whole life is ahead of you and it will not be like this forever, I promise you that. It is not selfish to leave your family but selfish TO leave your family...they love you and would never recover should that happen. It sounds like you've lead a charmed life and feel undeserving of it..why is that? Have you seen your dr.? I don't mean therapist, your regular dr..? It could be all chemical, a simple pill may help.