I'm not directly answering your question because I have never had a threesome or moresome during a comitted relationship. I have had 2 threesomes and a moresome, but never in a truly comitted relationship. Yes, you MUST maintain an open line of communication with your S/O...for me, I will openly say that I am a hipocrit when the thought of this comes up. With my wife (soon to be ex-wife), I would have loved to participate in a threesome just so long as the third party was a female, but I knew that I would NOT be prepared to watch her with another guy...PERIOD!!! It was a moot point, however, as she would never consider a threesome as an option in our sex life. Good luck and let us know what ensues, if anything!!!

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I wish all the ladies were pies on the shelf...and I was the baker because I'd eat them all myself.
I wish all the ladies were potholes in the road...and I was a dumptruck because I'd fill them with my load.