my grandma won't accept my sexuality?

[asdfghmk]

so i am 15, and i am 99% sure that i am bisexual when i was in 8th grade i liked this girl and i thought it was just a phase so i ignored it and denied it to myself, a few months later i had a dream about her very sexually so i told her and she liked me too and when we kissed it just felt right, like this was who i wanted to be with, to this day i still have major feelings toward her even though were not as close as before, whenever i finger myself it's mostly to girls, but i have experimented with 2 girls and one i enjoyed very much and the other not so much at all, but i can't get this girl outta my head and it's not a phase because it's been going on for 2 years.i've been with guys as well and i know i like guys for a fact. i don't want to be bisexual because my grandma won't accept it and i have to sleep at her house tomorrow because me and my parents made a deal and the whole time i'm with her she just talks about how much she hates gays and lesbians and they should just die, and i have to sit there and listen to it while i myself am bisexual, my parents know but they think it's a phase and if i fully came out they wouldn't let me have girls sleep over anymore. i don't know what to do i feel like screaming in my grandmas face that i am bisexual but she'd probably never speak to me again, i'm so lost right now. ever since i was little i've fantasized about girls, but people say that you aren't born with being gay or bisexual and most people don't even think bisexuality is a true sexuality, so can someone please tell me what i should do about my grandma and this situation and please send me an article or something proving that bisexuality is real