Bi boys who end up with girls are still bi
Bi boys who end up with boys are still bi
Regardless of who you end up with, your sexuality is valid.
It’s never too late to realize you’re bisexual, and you don’t need to have experience with people of multiple genders, or anyone at all, to know that you’re bi. You don’t have to prove your sexuality to anyone, you knowing that you’re bi is enough.