Help me out

I have got a really specific problem, i have crush on this one girl and she has been my bestie for over a year and a half now. We flirt a little and have nicknames for each other. Now i do wanna ask her out but im scared of rejection and that ruining our friendship but im also scared that she will tell her friends abt it and that theyre gonna make fun of me because were both in a close friend circle. If anyone could help me i would be really happy