it's scary

I wasn't really thinking about my sexuality since, you know, like most of us I was thinking I should be into boys and it was totally normal thing for me. But lately, I became more aware of who I am. Maybe I am overreacting but one day at school I was talking with my female best friend as usually and I suddenly started thinking about kissing her. But then I was like "C'mon, it's not a big deal, most people probably have similar situation". Later, I was thinking about it more and more, even when her t-shirt touched my skin I felt my heart beating faster. Then, I started thinking "how would I feel in a relationship with a girl?". At first I was scared but the more I was thinking about this the more comfortable it felt. "Holy crap, I have a crush on my best friend, and she's a girl too!", "What do I do? What do I do?". These thoughts don't want to get off my mind. 

I think I'm bi but I'm so scared of it. How do I tell my parents about it? I was thinking about telling my older sister first but I will only see her in a month and I don't even know how to say it. I just had to let this go off my chest