HELP SISTER AMBUSH

Let me give you a little backstory before I get into it. Two years ago my parents divorced. I have 3 sisters, one is a junior in high school, one is a sophomore in college and one just got married and is 25. I am a freshman in high school and I’m about to turn 15. When my parents divorced they let us choose where we wanted to live primarily. So I live with my dad because he is chill and cool and he lives in an area I like. My sisters chose to live with my mom. My mom is a lot more strict than my dad. So two days ago my sister who is in college came to surprise visit my dad and I but my dad was at work and I was kinda with a boy. So she just walked in the house and she apparently heard me (moaning) in my bedroom so she decided to just open the door and basically she sees me having sex with my boyfriend. (My boyfriend is 16). She freaks out and screams “Both of you put on your fucking cloths and get in the living room now!”. So me being super pissed because I was right in the middle of orgasming stopped and put my cloths on. When we are in the living room she makes us sit on the couch as she paces the room and tells us we are too young and we have no idea what we are doing and we aren’t being safe and al that stuff. Then I calmly explained to her that I am on birth control and we use condoms and that both of us have been tested for std’s. I also mentioned that we have been dating for a while and we were both ready to take this step and that we are in a healthy relationship. She then proceeds to yell at my boyfriend saying that he is taking advantage of me and that we should not be home alone without an adult. Then she makes him go home and she makes me take a shower to “wash away” my “slutty-ness” while I’m showering she is going through my room and takes all of my condoms and she finds a dildo under my bed. When I get out of the shower I’m yelling at her because she had no right. Then she puts in all on a plastic bag and throws it in the trash. The next day she just walks into my house again and finds me watching a movie in bed with my boyfriend and she loses it. She says that she is gonna call both of my other sisters and maybe my mom and then she leaves. When she comes back and I’m not home she finds my iPad witch is linked to my phone so she sees all my texts between my boyfriend and I. My sister sent me a text saying that all my sisters are coming over to talk to me about my “stupid decisions” and saying that if I don’t make the right choice they will tell my mom and dad. I haven’t right out told my dad “hey Dad Caleb is gonna fuck me but it’s okay because we are being safe”, but I’m positive that he knows that we are having sex because he took me to go and get birth control. I like sex, I’m being safe and responsible about it and I am emotionally ready. I have communicated about this with my sisters but they still want me to promise to stop having sex until I’m married. This is extremely hypocritical because at least two of my 3 sisters have had sex before they were married. I get it they are trying to help me and do what’s best for me but they aren’t and it’s honestly none of their business. I’m just afraid that they will tell my mom because she is very strict and she would absolutely get really mad at me and she would email my boyfriends parents and it would be very annoying and embarrassing for her to know. What do I do?