I guess the fact that both of us have an extensive sexual history with many partners, we just do not view sex as something intimate or restricted to special people. It is purely an act of pleasure.
While we reserve our love and intimacy for each other above all others, including our own families if it came down to it, sex is just for amusement. If she has a good time and is getting off, I am happy because she is experiencing something pleasurable, and she feels the same way about me being with another woman.
Your attitude tells me that you are pent up sexually, and have difficulty enjoying the act for what it is, and are hung up too much on what it represents to you personally.