He Has A Long Lost Daughter-OPP

A woman just found out that her husband has a child from before they were married. She feels lied to and completely left out based on how he is dealing with the child and her mother.

Mike & Kate-
I'm a married mother of 3. My husband and I have been married for 12 years. Our kids are all under 10. I thought we had the perfect family and the perfect life until this summer. One day my husband informed me that his daughter was coming to Idaho for a visit. Apparently he got a girl pregnant when he was 18 and they gave the baby up for adoption. Fast forward 18 years and this girl came looking for her birth parents after she graduated high school in May. The adoption was closed but I guess thanks to Facebook and the internet she was able to track down my husband after a year of looking.
In the 14 years I've known my husband, he never, ever told me that he had a baby that he gave up for adoption. He didn't even tell me that she contacted him in May. He waited until they had chatted for a few weeks and then suddenly dropped the bomb on me that his long lost daughter was coming for a visit. I have been struggling with all this ever since and am just trying to keep up and help our children understand this very confusing situation.
The birth mother also lives her in Idaho. Since this girl arrived in Idaho, my husband has been spending tons of time with his daughter and the birth mother. Me and my children are not included. She stays at our house when she is not with her birth mother 2 hours away. But I feel very left out. It's the three of them going out doing things.. They even went on a camping trip this summer. My husband claims that he needs to get to know his daughter before he involves our children. He claims he needs time to bond with her. I understand that. But why does the birth mother have to be a part of that? Can't they each bond with her on their own time? And if this girl wants to get to know her birth father, shouldn't that include the life he built since he had her? You can't separate us. But he says that they owe it to their daughter to give her the one on one attention that she never got from them.
I'm also struggling with the fact that my husband never told me he had a child. I worry about what else he is hiding from me. That is a pretty big secret to be hiding all these years. His parents even knew and no one said one word to me. I feel like I've been living a lie.
Do you have any advice for me on how to handle this situation? Am I justified in being upset? How do I get my husband and the father of my kids back?

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