I feel so lonely all the time. I don't trust anyone, not even my best friend?

Well... The first thing you've got to do is drop those "friends." if they didn't say anything to comfort you when your grandmother died, then it showes how they don't have feelings. I know it will be hard but those people don't deserve you. A year ago I was somewhat like you, but I got through it by knowing that my life can be better if just wrote a list of what i want to be and accomplish it. I haven't finish yet, but i feel better than ever!! Try reading this book called "The Me Who Nobody Knew" it deals with some of the problems you are going through.