Attachment problems

Hi all, I'm an adoptee and was wondering if anyone understands this. I was adopted age four, and remember some things from before. My birth mum left me alone alot, and I was simply neglected in that respect. Now I find myself wondering if there's just something wrong inside me. I can't seem to attach to someone without needing reassurance all the time that everything's okay, and if it's not then I worry. I have panic attacks if I have an issue with a friend, in a relationship etc. thinking that everythings going to crumble to pieces and we will end up hating eachother. It seems like a ridiculous notion saying it but I really can't control it. I really freak if someone suggests that theres something wrong, they don't want to go out/do things together. I always come to the conclusion its all my fault. I feel that something went wrong when I was growing up that left me really needy, I've never had a good relationship with anyone, friendships always fail in the end. I just feel so alone because of the way I am. I don't feel like I need to be with someone all of the time, I can spend a couple of hours alone at most then I start to become ill. I simply need constant reassurance and that doesn't seem right to me, like other people don't think the same as that, or am I just too insecure. Any advice or personal experiences would be great, just wondering if this is a normal reaction and if anyone knows how to alleviate these feelings in any way.