I think most have a 'real' and 'social' you. Unless you have known someone for a long period of time, you have a natural armor; a self protective shield, that protects you and your emotions.
You may do things socially that you wouldn't do normally do for a number of reasons. Being politically correct and not offending others are a couple.
When you're with someone you trust, it doesn't matter what you say or do. They are going to have your back no matter what. There is no pressure.
However, to some, none of this matters. They are completely confident and being true to themselves at all times is something that just comes naturally. They have a "take me or leave me" mentality.
I can totally be myself anywhere and anytime with my husband.