What is wrong with me and why am I like this?

My head is like chaos... it is like suppressed thoughts all going round in my head at once. Sometimes I get flashbacks of bad things that have happened in my life (being bullied etc) and it is making my life hell. I have a new friend called Sharon and she said I could come up to her house but when I got there she said she didn't want me there so I suddenly felt even worse... like intense rage and went back home and started slashing my wrists to get rid of all the pain. On top of that, I have a 'friend' that comes round everyday just to use my internet connection and drink my tea and when I tell him to leave or when I am going to go out he starts complaining and saying that I don't think of other people so I am forced to stay in while he downloads games but I don't know how to get rid of him because if I try too hard he shouts at me. I feel like I am a messed up individual in this chaotic world. I am confused and don't know what to do anymore... The only thing that really briefly takes my mind off everything is visiting my local graveyard and sitting on the bench. I talk to the dead people, they are the only real friends I have. My stomach and chest doesn't feel right, I have often thought of what a relief it would be to stab myself in the chest, not just to die but to get rid of that numb feeling that I have in my chest.