I understand your need to get answers since your husband has not been forthcoming and you've had to find out details on your own, but if he broke things off with her abruptly, she may still want him back and you will have no idea whether she will say things to make things worse for you that may not be accurate. I would rather put effort in getting your husband to open up more. If you come at him screaming/yelling (understandably) he will only get defensive and fear telling you details. If you can have some calm discussions that are focused on your feelings of deep hurt and betrayal, he will be more likely to want to help you get through it by talking more openly. IMHO talking to her will only add to the confusion. I know this sucks
but the positives are that he realized he still loves you, he broke things off with her and he wants to work on your marriage, so you are both in a good position to get through this & have the opportunity to make your marriage stronger than ever.