Was your friend a good friend before she became 'positive'?
I'm just wondering if she has always been this way, or if it's just been recently? I think this is an important factor in determining how much you want to try to make thing better.
I do not know if this is true of you, but if this was the 1st time you confronted her and made yourself vulnerable, it is actually predictable for her to 'reject' you.. She is probably shocked, and not used to you being this way!
This is a suggestion only, but if I were you, I would give her some time out, and see if she doesn't come around and want to work out, and take some responsiblity. At least, then, if things don't seem repairable, you will not have any regrets or doubts.
I think that it is not wrong to be selfish, but it is to be self-centered. What I mean is that you need to take care of yourself, your needs, and have good boundaries. If you don't, you are allowing other people to step all over you.
It sounds like this friend was doing that, but you would be the best judge of that.
take care