"Coming out" as bisexual

So I've always felt attracted to girls and I've discovered that I enjoy hooking up with girls just as much as guys. I've been talking/flirting with this girl and I'm super excited we're going on a date this weekend! The only problem is I don't know how to tell my best fiend that I'm bisexual. I usually tell her everything and it's feels so weird to be hiding this part of who am from her, but I'm worried about she will react. I think she has more conservative views and I don't want her to be freaked out or think of me any differently. Does anyone have any advice for how I should deal with this? Also any advice for dating girls!? This is super new to me.. By the way, I'm in high school so I guess that kinda adds drama to this.. Thanks! :)