Having protective and over bearing parents?

Hey! I’m gonna be 18 next month and this has always been a slight controversial discussion with my parents . I’m obv a girl and I’m an only child but I’ve been with my amazing bf for over 3 years . I rly want to sleep over his but my parents won’t let me , even when I’m 18. I’m so upset and frustrated bc like sorry mum but it’s not like that will stop us from having sex if that’s what she doesn’t want and it’s not like she’ll hold responsibility over me if anything does happen once I’m an adult. Idk what to do to convince her bc she says she’ll kick me out if I sleep over his . Also , me and him r planning to go to Italy next year (that’s my b day present) but I’m so worried how she’ll react to it . I hate feeling trapped and unable to live my life . I feel this constant financial threat every time I want to do something more independent.