I am a stay at home mom, so I don't have to worry about being out at work. My husband, Avatar, is out to his "work wife" but no one else. He doesn't really associate with anyone else at work. Busbuddha's wife is out to many people where she works, and has lost most of her friends because of it. It's unfortunate.
As far as telling our 11 year old, he knows his sister is biologically Busbuddha's daughter, and we speak very openly and honestly with him about sex and everything else, so not telling him about the 4 of us is difficult for me. I pride myself on being honest with him. Busbuddha and his wife are my children's godparents, and they are here ALL THE TIME, so he definitely knows we are best friends, and he likely knows more than that is going on. He sees us all being affectionate with each other even when we try to keep it under wraps. And he also knows we spend the night at each other's houses sometimes. He is a smart kid, but not one to pry.
Thanks for the welcome!