how did you and your partner first start talking about MFM threesome?

It was many years ago before I was married, a coworker came to my office one morning and said "you have to come with me at lunch time", so I did. We went to see a woman he knew who was waiting for us on the sofa wearing something that opened up in the front. We spent some time playing with everything she had then headed for the bedroom. We both entered her vagina at the same time which she loved. We kind of got an alternating stroke thing going and it was a lot of fun but I think she got a lot more from it than either of us did. It felt kind of weird rubbing against his penis in there.