You are probably better off just minimizing your time with your husband and carrying on as usual with the rest of your business. Until you know what his intentions are and if he truly intends on working on your marriage, you want to keep from getting hurt any further by him.
If you and your husband do end up working on your marriage together, then any questions you have about what he did with this woman are ok to ask. Some people feel that leaving it all behind and not talking about it is better, but your husband allowed another woman into your marriage. That makes anything he did your business and therefore up for discussion.
It is very sad that this woman is a marriage counselor. She really should understand how much harm she is doing. But personal feelings and professional feelings can sometimes be very separate things.