Im sure there are many factors at play here. Im my own case, when I began my transition four years ago, I always thought that Id remain a, Lesbian, attracted to women. And while that is still largely the case, a bit less than two years ago now, my sexual orientation made a sudden shift to where Im now Bi/Straight(hot for guys). I never had that much of an interest in guys before, beyond a general curiosity w/ male genitals. I never considered myself to be, Gay, as thought of being w/ a guy as a guy made me ill,. However the thought of being w/ a guy as a woman sent me into orbit,. All of a sudden I wanted someone w/ a big, muscular, and hairy body,,. However I dont feel that it was the Estrogen I take that had much to do w/ this. Im more suspecting that it may habe been the Progesterone I also have been taking for just ovr two years. And I have a possible theory as to why this happened; I initially started Progesterone to help w/ my breast development, which initially I had only seen a minor improvement in. But then I read some suggestions that if I switched taking from taking Progesterone orally to taking by rectal insertion it might improve things, as this was considered a far more efficient means of delivering directly into the blood stream. Within a couple of months two things happned; My boobs went from Bs to Ds(thank you, Boob Fairy :) ), and guys suddenly started looking very, yummy,,. What I think may be going on is that since Progestrone is present in Cis women when they are pregnant; it serves to help "mature" the breasts to prepare them for feeding the new baby. I suspect that my brain may be saying, ok so you want to get prego? You need to go and find a guy first,.. And I will futher add, that Ive also been experiencing some feelings of what is sometimes called, being baby crazy; thinking about being pregnant and having a baby, which fortunately/unfortunatley, just aint going to happen for a number of reasons,,. My first time w/ a guy as a woman, totally lit a fire in me that continues to burn ;)