Okay, so a similar situation happened with her ex-bestfriend. You're right to worry, if it happened to that person there's a good chance it can happen to you too.
I'm not advising you to break up just for the sake of it, I just think the way things are it may be for your own good, as I don't anyone to end up like what happened to me. Ending a relationship is hard at first but eventually you should be able to move on.
HOWEVER, if things are going quite well at the moment, hold off on that option. But can I ask you if you think the current status of your situation in that 'things are going well' is going to last? From the way you're putting it you don't believe it will.
I don't think you should break up the way you put it by saying all that stuff, but sooner or later you're going to need to have a serious talk with her about the future of this relationship and any problems attached to it (if you haven't already), as the way things are now it's only going to get worse. I know most girls and sometimes guys try to avoid this talk, but from past experience avoiding it tends to be the biggest mistake as by avoiding it couples miss the chance to fix any problems in the relationship.
Have this talk no matter what! I know you don't feel as though you can lead a relationship, but there are times where you just have to, for the both of you. It's up to you to help her and change her for the better, if you want to save her and your relationship.
Remember my advice is just advice, you know the situation better than anyone to make your own decision. I hope things go well for you.