I know exactly how you feel, i have the same problem.
When I meet a new person I instantly become attached to them. I feel as though I have the potential to love this person (whoever it is at the time) wholly and unconditionally, despite there faults and flaws, in my eyes they are perfect and I treat them as such. I become addicted to them, needing their constant attention and reassurance.
This attachment problem has obviously caused me alot of problems in relationships, in one relationship- caused me to be used, as he could see this all unfolding and abused it, having me basically pay for everything, his rent, drug habit etc. In my last 'relationship' in ended it, it was long distance and so obviously most of our communication was internet/phone based. It got to the point that I would get upset and feel abandoned when he had to get off the phone, despite talking for several hours.
Despite being obviously aware of these problems I can't seem to break the behavioural cycle, it seems as though I can only value people at the two extremes, either not at all, or they are my entire world. And when they leave my world shatters
I think it is because I really don't have anyone else in my life, no real friends or family, no other social support. So they instantly take on all of those roles.
It is somewhat comforting to see that I am not the only person suffering in this way.