My mom...

Okay so I'm 18 (turning 19 in a few months) and my BF just turned 19. We've been together for 2 years. We finally had sex last month (only did oral before) cause I wanted to take my time and be prepared etc..my mom doesn't know but when I asked if I could go to a music fest overnight with him she basically yelled at me saying that if I do I'll have sex and he'll leave me cause he'll have less respect. I want to have a mature conversation with her about this because she often says things like if I have sex I'm breaking her rules and she'll stop paying for my schooling etc...basically makes me feel like I have to choose between her and a sex life which isn't fair. I go to school away from home so I do have my own place. I pay for my own birth control, I'm an adult and my boyfriend and I had talked about sex for almost a year before actually doing it, we were well prepared. It really hurts me that she talks to me like this and threatens me when my choice about having sex does not impact my ability to be a good daughter or person or get my degree etc. I want to talk to her because I don't want to have to sneak around to go places with my boyfriend (we like to take trips and stuff together but we've never been allowed to go alone just cause of my parents). I know legally I can choose to do what I want but I would rather have my parents approval and agreement even if it is my money. I don't want a bad relationship with my mom just cause I want to have sex with my boyfriend, it just seems really unfair. How do I approach this? Whenever I try she says he's probably pressuring me and that she doesn't like him even though that is so not true.