how did you handle it and still be friends?
Too many factors, too many variables. Like any relationship, each one is different.
Major thing, communication. She probably wouldn't be your ATF if something didn't "click" in the first place. That most likely means that the two of you have good communication. Don't hold it in, communicate. Chances are she's probably picked up on the way you're thinking already.
Be willing to walk away, and don't burn any bridges in the process. Who knows, after a cooling off period, things may start up again only under a new set of circumstances, and be better than before.