Some of my earliest sexual fantasies involved two or more women. It's become a cliché that all men wish they could have two women at once and I'm not going to deny that I fit that mold. I've even occasionally wondered how I might make something like that actually happen, though it never went past the musing stage.
Then I actually had sex for the first time and realized that I may not be up to the task of pleasing two women since focussing my attention on just one seemed to take up most of my energy. Of course, the idea of two women pleasing me as well as each other continues to be a favorite fantasy.
As I started to be more aware of my bicurious tendencies, my fantasies, roleplaying and erotic writing started to include encounters with transwomen. I figured if I was going to explore someone else's penis, it would be easier if it were attached to a beautiful T-girl.
I guess that's what they call a slippery slope because after a while, the idea of a ménage with a woman and another man soon followed. At first with just the idea of me and the other guy pleasing the woman but soon we were pleasing each other under the hungry gaze of our lady friend who, of course, was incredibly fascinated and turned on by watching her two male lovers having sex with each other.
While I still fantasize about the classic MFF threesome from time to time, and enjoy thinking about being with beautiful transwomen, I have to admit, the majority of my personal sexual fantasies are of the MMF variety which constitutes the main theme of my favorite erotic writing project, "The Kendra Collection." It also lead to my first attempt at writing an MM story which I have discussed elsewhere.