A secret I'm carrying right now…

I really really like my best friend, like honestly I think I'm in love. It's so scary to think or say and I have no clue what to do cause I am almost sure she doesn't feel the same way. I know this isn't some disaster but I really need advice. I don't know if I should tell her or not because she really is my closest friend and I don't want to lose her. I'm genuinely terrified and have no clue how to get this anxiety to go away. Everytime I see her I just get this pit in my stomach of like "maybe she knows" and it's honestly miserable. I have no one to tell because everyone I know would tell someone and then she would find out. And yes, I am saying this as a girl as well