This Kid At School Is.. Obsessed With Me?

Okay, at my school a new boy came and my group accepted him because he was rejected. Then we sorta ditched him because he was really weird, as in autistic or some other mental retardation…
They ditched him because he would apparantly cut himself, and threaten to commit suicide if they ever told anyone and he also played with a pocket knife…
He also is obsessed with death and suicide. He randomly walks up to people and hugs them, holds their hands, and does really weird things… he freaks me out. He also death stares EVERYONE for no reason! hes so weird!
And he would come up to me and ask me random question like ‘ are you cold?’ in summer and ‘ whats wrong?’ when i was perfectly fine..
On facebook i added him and was nice to him, because i felt sorry for him.. Then he was obsessed with me and would inbox me how much he loves my personality and how im always smiling and would chat with me ALL THE TIME.. And it freaked me out and he was soo annoying so i deleted him…
Then he like stalked me and tried to add me again the same day!- how would he know i deleted him?!!?
I ignored it and he sent a few more and i ignored those, then he inboxed me and said “Why did u delete me i tring to be nice and you delete me WHY DID U BLOCK ME WOW GEE GREAT FIREND YOU ARE I TRY AND BE NICE’ ( he has a mental disorder so he doenst quite speak properly.. )
Then i blocked him because it was all to much. Then everyday at school he started death staring me and would come up to me and yell why did you block me?!? so i said ‘ well.. i got a virus that delets and blocks my friends and my computers screwing up’ , because i didnt want him to like kill me because hes emotionally unstable…
Then i was talking to a friend and they said that john would obsessivly ask them if i was online over facebook..
Then John started messaging me on petville!!!!! giving me his phone number and email and begging me to add him again and most recently it said this.. ‘i dont know if you hate me but -so and so- said that u do i need me -email- or -number- i dont know any more you are my sunlight but now there rain’
What do i do?! I cant ignore him, or say stay away, because he is the type of crazy that would kill me at school!!! Help!?!?!?