At work, I am a pretty private person. I don't talk about what I do outside of work hours, and nobody has a clue about the other women in my life. That's just the way I am.
Yet, I am extremely open. We are open to our friends, our family, our kids. On Facebook, I'm "in a open relationship" with my wife, and have link to my girlfriend's profile under the label "My lover". *grin* I really have no fear of any repercussions.
I suppose I have always treated the work environment differently than the rest if my life. I don't get to choose the people I work with, so I don't feel the need to associate with them in my own time.