It doesn't have to be so black and white. Waiting for her to break up with him would be silly, but there's no reason to torture yourself. Stay friends and date casually with others (I think you need the practice). Maybe an opportunity will present itself later.

Timing is important, obviously. Right now is not the time to confess your feelings for her- and why would you do that anyway? What is she supposed to do with that? You would put her in an impossible position.

The guy who told you to do that is either crazy or mean.