Same sexual things all the time get boring. It's the primary reaosn people cheat. Routine sex is dull. New sex is hot and exciting. If you've been into women primarily, may find the men with the women in what you usually enjoy looking at hold some interest too. Evolved my own bisexuality this way. Lots of sex and fantasy about women, but men were also present as in most porn, so over time I wondered, eventually experimented and realize sex is just sex.
I actually maintain there are no sexual orientations but rather everyone's situationally sexually fluid. Prisoners 'make due' with same-sex sex despite identifying as heterosexual, actors play gay roles though straight, people "experiment," top may id as straight reasoning everyone's mouth and ass feels identical (rightly so imo heh,) whereas bottoms are "gay," etc.
There's so much overlap in our sexual terms what is or isn't this or that depends on the indfividual speaking. Is having a gay fantasy an indicator of being gay, if so is a lesbians ex fantasy if male an indicator of wanting to be a woman? Who knows. Who cares though is more to the point. Sexuality exists on a spectrum. It's not all one thing or another.
Just as only about 3% of sample groups identify as exclusively gay, I think it's about that for exclusively straight. Everyone else is somewhere in the middle.
Are in fact 6 biological sexes for people (not just two, male and female, look it up,) so lots of sexual possibilities to be enjoyed. Why int he world should we limit ourselves to 1/6th the possibilities if we enjoy sex?