One more question ODC....... is she the type of girl that has a dominant personality? take-charge go getter type? girls that are really sexual can be like that. If so, then whether you have more $$$$ or are bigger than her bf won't really matter.
But you still need to find out what is keeping her with the other guy, she could be just stringing you along and if so, it might be better to just find somebody else but I'm not in the place to answer this.