CF What should I do?

Dear Steve and Shirley

I never thought I would be writing to you. Several years ago I met a beautiful woman from DR. We hit it off perfectly and have been dating ever since. She moved in with me within a year. Sh always talked about her twin sister and how they loved each other and how they used to share everything. A year later she asked if her sister could come and stay with us for a vacation. Of course I said yes. So she arrived and was as beautiful as her sister. They indeed shared everthing food, clothes,conversation. I came home from work one day and they both were in our king size bed watching TV. I must have looked surprised. My fiance said “its okay come on with us. I did. Well, my fiance started a session with me while saying her sister won’t mind. To my surprise her sister began to participate…..What should I do?