Bisexual

Meaning that you fall for both genders.
People who are bisexual can fall for both girls and boys.

If you're a boy, you can fall for girls and boys,
if you're a girl, you can fall for boys and girls.

Some people might have a preference, like girls might have a preference to fall for boys but can still fall for girls, but a bit less than that they fall for boys, but they can also have a preference for girls and fall less for boys.

Same goes for guys/ boys.
People realize tha they're bisexual quite quickly, though some people might deny it since it comes at a random time or that they've been straight theire whole life so now it's like it's just a mistake or maybe a small phase.

And yes, bisexuality (and all the other sexuality's), can accidentally been taken by a mistake and can actually be a phase, but if it's been longer than 4 years you should start to realize you're actually bisexual.

"I'm bisexual."
"Oh! So you fall for boys and girls?"

"I have a preference for girls, but can fall for boys."