Good morning, D.! I've read through the responses because I wanted to know how other mothers felt about this compared to what I think. Quite a few suggested counseling, even so far as to specify Christian counseling, but not one mentioned FORGIVENESS. We live in a very modern society where women are strong enough to stand up and strike out alone, but do you really want that? I am a divorced parent, but my decision was made after I was absolutely sure there was no hope for my marriage. I know I made the right decision and I haven't regretted it. You have only just found out about the situation, and I know that you are feeling that the only one you want comforting you is your dear husband, minus all the insecurity and pain he has caused you.
I suggest sitting down with him, somewhere quiet, maybe go out on a date to someplace cozy so you can really talk. Explain that you want to tell him something and that he should really think about what you're going to say. Then start in on the dangers of sexually transmitted diseases and how they could affect an unborn baby. I don't know your husband so I can't say whether or not he started a physical relationship with this woman, but we'll just give him the benefit of the doubt in this case. Tell him that you love him and you want to raise your baby together as a family, and that you want him to open up and tell you how the whole affair got started. It could be that after all the time alone he had with you, he suddenly was playing second fiddle to morning sickness and then changing hormones, etc., etc. Maybe he missed how it used to be and chose to open up to a friend at work and it just went from there. We don't really know how much the other person was involved, so it's not fair to judge her. Perhaps she thought she was being a shoulder to cry on. He could have gone to her with the old story, "My wife doesn't understand me, blah, blah, blah..." Women, unfortunately, fall for that all the time.
Just ask yourself, are you going to let this woman come between you and your husband and your future as a family? Is she really that unique that your family has to fall apart? She shouldn't be the one to control what happens to all of you, especially that little baby, who has no say at all right now. Your little angel needs you two together to keep him safe and show him what a strong family is. You have the answer right now, by just wanting some advice from us, total strangers, on how to handle this situation. That alone is enough for us to know that you want to stick it out. Isolation (not wanting to share what's going on because of the fear of people judging you or your husband) is just keeping you from getting peace-of-mind from your friends and family. They are there because they honestly care about your health and well-being, and because they love you, they know that you need their support, not a verbal attack on your husband. Don't worry about someone thinking bad about him or your marriage. If they do, that's their problem and you can simply thank them to keep it to themselves. You don't need that kind of negative feedback.
Have that heart-to-heart talk, forgive him for turning to another woman, and then continue on together. Some of the ladies have suggested going on dates. That sounds like a fun idea. Rediscover why you fell in love in the first place. You're a good person who didn't deserve this, especially at this special time in your life. This is just a huge bump that you've encountered in your life, and it's just one in a series of events, good and bad, that will eventually shape you to be the beautiful individual that you are. Motherhood and marriage can be difficult paths to follow and right now you really need your husband's help. Be the bigger person and forgive him so you can move on.
Good luck and God bless!