How do I accept that fact that I am a horrible person and it will never change?

First off, your not a horrible person at all, i like you and i only read a short question you asked, but you don't seem nasty or bitter even though it seems you have been unlucky with the people you have around you. Things will get better, and you will meet some nice people in your life that you can form bonds with, don't bother yourselve with what your grandmother thinks she dosen't sound like a nice person. It only matters what you think, your still so young, and things are bound to pick up for you, just hang in there!!