Most Helpful Girl
You pretty much messed up that relationship. For girls, it is fine if you still meet your ex, but at least (that is, if you like her) be honest with her and let her know that you are doing something with your ex even though she has been ignoring you. Then you come clean and she knows that she can trust you, also if it hurts her that you are visiting your ex. Anyway, there are other things you should consider too, if you really want this to work. First think why you really want to be with her, make a list. Afterwards, you can read her the list or tell her in a nice way, why you want her, why she is the one for you and that you only care for her. BUT be careful that you do not add things, which do not come from the heart because she will find out eventually.
My opinion: Just be honest and let her calm down, it's the best you can do at this moment in time.