I’m bi

I’m bi but my best friend doesnt know... not only doesn’t she not know I’m bi she doesn’t know I was in love with her for years.. I never said anything because I thought she was straight. Well she just told me she has a gf and I feel so angry with myself. Also she asked me to prom today what do I do? Should I tell her? Do I wait till her and her gf aren’t together??

Side note we used to give each others hickeys but I didn’t think it was anything and we never talked about it again