Most Helpful Guy
It depends on what you mean by talking about your ex.
If you mean talking badly about her with others, I think you should never tell really personal stuff. You have to respect their secrets even after a break up. This does not mean you cannot say anything about your ex though.
For example, if you just want to talk about how your ex was in the relationship or anything which is not extremely personal, it is fine. You can talk about thing that your ex did that you liked or didn't like or stories you shared with her, just to name a few. You should not tell things about your ex you are not comfortable with telling others (except if it was something she did to you which nobody knows. Then you have to tell it.). If friends are messing with you and want to know how she is in bad or something, just don't answer. They don't have the right to know and you aren't obliged to tell anyone stuff like that.
I hope that helped. You question was a little vague, so my answer might not be what you are looking for. if that is the case, please ask me something more specific!