Yeah, society projects a feeling of shame on a person who appears to be cheated on and doesn't know it. When I was in my triad, this was one of the worries of my first girlfriend. Neighbors and people at the resturants we go to would judge her as being "cockold" (I dont think there is a word for a woman).
At first we just hid and PDA and all acted as good friends. But my other girlfriend kind of felt left out since she had to act as a friend. So we went the other extreme and showed PDA while all three of us were around. So neighbors would just assume we were kinky instead. (I guess that is better than neighbors feeling synpathy for you.)