Talk to parents

How should i talk tp my paremts about sex. They are super strict and get mad easily and wen my sister told them then she got grounded for eternity i just want my mom to be a part of my life and society has made it so hard to live these days. I had sex once w my bf and i want to tell her so she doesmt find out another way. I dont want to get in super trouble and i dont wamt to break up. How should i talk to her?