So frustrated.

I've been so frustrated lately, my younger sister who's fifteen had sex a few days ago. It frustrates me because she is the type who always said and was adimit about not having sex before marriage. I was fifteen when I got my FIRST KISS. I  am just really mad, but at the same time I would never have sex with a random loser. Still so mad though and I don't even understand why. I just kinda hate her rn. Someone advice, counsel?? :(