Do I tell my mom?

I'm 18 years old, and currently live at home with my mother. About 2 years ago I asked my mom what she would ever do if I ended up pregnant and she said she'd kick me out of the house. Me and my boyfriend of 1.5 years started having sex about 4 months ago (my first time). I come from a Christian family and I know my mom would highly disapprove of sex before marriage, and I'm scared that she would kick me out or be too upset to even talk to me. I love my boyfriend, and I love having sex with him. I don't want to stop, and I don't plan on it. Is this something I should tell my mum though? One part of me says I'm an adult and I'm allowed to have a sex life without my mother needing to know, another side says I should be open and honest about it. I just don't know what to do