Relationships can change gender. If gender is anything, it's a way to identify one's self in the various, never-ending mating games taking place in humanity. If you enter into a lifelong, monogamous relationship, it makes sense for this to change the way you identify in the game.
boy want gf to feel like man, girl want bf to feel like woman, woman want man to feel like girl got kinda weird with boy want man to feel like girl and woman want girl to feel like man but the basic mechanism of relationship changing gender is the same
