Whats wrong with me

I’m not new to this site I’ve been here before on a different account. I left because I thought I got better. But today I just kind of broke down and I don’t know why. My sister is graduating from highschool I’ll be a junior next year. It all hits me pretty hard because I’ve never really had any friends so id always hang out with her. And this year I talked to some of her friends which I’ve even considered to be my friends but I don’t think they feel the same way. Anyway I just want to say I’m a piece of shit who treats people like trash for god knows what reason and deserves to die. I can’t even help a little girl who needs my help right now more than anything. God kill me now.