Great advice Anne.
Mue, I am having the exact same issues. I was starting to think I was going loopers because everyone around me was so needy and dependant and needed my constant attention and reasurrance. It was emotionally exhausting- this year alone I have shed at least ten friends. I told T about it and I said it must be my behaviour beacuse everyone else can't be like that. I wanted to know what I was doing to attract these types of people and of course it is to do with healthy boundaries and how I react to people who invade my boundaries... I open the door and let them in. So now the door stays firmly locked but one or two creeps still get in.
Anne was right though when she said that this friend hasn't given any warning signs and she does seem genuine, just because you have had some pretty bad experiences in the past try not to let them paint your future.