My best friend has odd behavior?

He's been acting like this for a long time and it's starting to concern me. He's a kid who I can't read easily and sometimes I doubt whether or not he cares about me. Sometimes he'll be really nice and will make me happy and cheer me up when I'm sad, or some other times when I need him to help the most, he'll just say 'whatever' or just complain how I'm over emotional. I agree I can be over emotional, especially for a guy. But I don't believe that's a bad thing. I think it's ok to be different that way. My best friend used to be equally as emotional as me, but by the looks of it, I fixed it for him. He's not sad anymore. He says he never feels lonely and he rarely hangs out with any friends over the Summer. He's my best friend and next year we're going to seperate high schools and we won't see eachother as much, so I try to spend all the time I can with him (about once a week for 6-8 hours at the most). I'm afraid I might be bothering him. It's hard to get questions out of him because whenever I tell him that I'm worried or want to know how he feels, he thinks it doesn't matter, or he clearly just lies to me and says everything's fine. I've told him multiple, multiple times that if he ever needs help, or someone to talk to, he can come to me. He never does. He did say to me he isn't very sociable and when he goes on his computer, he never goes on any IM or anything anymore (he lives far away and I hate the phone) so we'd usually talk on the computer. But he just stopped going on IMs because he thinks I'm going to bother him about something I guess... I can ramble on about some stuff I'm worried about, but it usually comes to an end at some point. I've gotten more emotionally stable than I used to be. I don't know what I did wrong and he won't tell me. I'm afraid I made him upset and I don't want to make it worse. What did I do wrong?