How can I tell him to stop without being mean?

[ForeverYoung]

There's this guy who I have on facebook. I have never once met him in real life but he went to the school I used to go to. He also follows me on twitter. Once he commented on my status, and I was nice to him back, since I try to be nice to people, but being nice to him just started up a shitstorm. He now made me his 'sister' on facebook, posts on my wall at least 2 times a day, posts awful country songs on my wall and tells me I 'missed' his post if I don't like the post, he even comments on and likes wall posts that are from my friends TO ME and don't include him AT ALL. He has liked comments that my friends and myself have made on wall posts that are from me to my friends. I honestly believe that he reads EVERYTHING on my wall, and I am not exaggerating. I never thought that just being nice to someone would make them become so clingy and obsessive. He's nice, and I know he means well but it's honestly getting VERY annoying and creepy. I don't know how to tell him to stop because I have trouble being assertive, and I don't want to hurt his feelings because I don't think he has many friends, if any at all. I really want this to stop though. It's getting to be way too much! I don't spend all my time on facebook like he apparently does so I can't just sit there and reply to all his posts and listen to his crappy songs! Does anyone have any advice as to what I can do without being outright mean or just ignoring him? Thanks to anyone who helps and sorry for the run on sentences!
I don't want to just block him because I think he might have some kind of social disorder, and I think that would REALLY hurt him. Like I said, he has essentially no friends.
Also, when he tried messaging me on facebook and I didn't reply he tagged me in a public status asking the same thing he had messaged me about. =/ and when I only liked his post on my wall he complained that all I did was like it.

[impish knight]

You have been bit too nice towards him for your own good, just block him and get on with it

[notme]

This kid sounds lonely and just needs people to acknowledge his existence and you reached out to him,you gave him purpose and hope to develop friends but he needs to develop his own healthy relationships with other people not just you,but if you delete him he'll be hurt,but if you take the time and ask about his school,hobbies,family see that he just wants to talk and be friends then u should. But the minute you notice that he puts your friends and ideas down and it seems he wants to isolate you from what makes you happy,you delete him out your life.Additional Details warning if he easily get upset and makes you unhappy or disappointed because you have a life and he doesn't then tell him or delete him out your life.