I agree with GEL's last post. Stay calm. Do not rant and rave. Do not cry or get upset in front of him. It will make you more unattractive to him and then he will be looking at your behavior and not the issue.
Talk firmly and calmly. EA's and PA's have happened with many people and they have made it. It you take a "this is the end of the world" mentality you won't handle it as rationally. Men need to be dealt with rationally.
That you confronted her is fine, but really the issue is with your H. He can choose to break it off. That he defends her and what he is doing shows a strong tie. But, it can be broken.
Great you are going to counseling. Great step. Let us know what comes of it.
Michelle has some great things in books and on site about what affairs and divorce will result in. I think he needs to know some of those things...they are 1)Does he know te pain that will come to his child as a result of an affair? 2) the grass is never greener on the other side..Michelle says it eloquently and states some great things in the first chapter of her book "Divorce Remedy"....!!!! I've given the book to a few people...it is eye opening. Read it..if you haven't...!!!!!!! Very good book, very helpful! Educate yourself with more than we are able to offer.
Much love sweet girl...don't give up! You can do this. Do the right thing. Act in a way that you won't later rather. Don't say things you may later regret. Many times my only strength has come through the Bible and from God's incredible help to me. I would have NEVER made it without that! You can make it dearest.....