I think I'm a biual with a crush on my best friend?

I've had a girl crush before, but I was 11 and it lasted for about a week, so I thought nothing of it. But I've never been repulsed to the idea of s or anything, as in I've considered myself as one and wasn't thinking ''eww i'd never do that''. Anyway I've developed a crush on the most important person in my life now and I don't know what to do because there is no way I can tell her, it would definitely damage our friendship. And I don't even know if I'm . She also has a boyfriend and I have to see them together and pretend to be happy for them when really I wish i could take his place. What should I do?