I'm a bisexual(girl) and i fall in love with my (girl)best friend

it all started back then when i moved to my new school , then suddenly i know her by accident but it turn out that she's just relatable to me , and shares alot in common . we've been known each other for about 5 month(as i can remember) and i really love her , and this is not just a girl friendship thing , it's more than that . i often daydreaming about kissing with her but it just strange because she's straight ( at least that what she said ) but sometimes she's doing a 'not so straight girl' things to me and i'm well, aroused.i really want her to be my girlfriend but what should i do ?