Sexuality isn't a choice. But some people don't know or acknowledge who they are until life forces them to. Human existence is stifled unless people allow themselves to grow and evolve, and life circumstances don't always present the right opportunities.

Also, cross-sex hormones are powerful and will change the human body. The brain and body work together.

Lesbians who transition and become gay or bi men: Testosterone is a hell of a drug. Testosterone is the first hormone that is checked by doctors when women experience low libido or low sexual desire. T is responsible for those urges. High T-levels in women are a medical disorder and/or permanent. So lesbians who take it and suddenly like men were either bi deep down all the time and didn't know, or the hormone influenced them to be different.

Straight men who transition: Estrogen changes physical attributes, but it is NOT strong enough to override T, the hormone responsible for libido and desire. So either these men were bi or gay deep down and didn't know, or they are imagining themselves AS WOMEN and using other men to affirm that. So they are HSTS (homosexual transsexuals) or fetishists. Fetishes exist outside of sexual orientation.