I need help

I’m 20 going to be 21 soon. I still live with my parents. I’ve been hooking up with a guy and my mum has no idea. I stayed over at his place one night and I told my mum I was having a sleepover with a friend. My mum and I have a good relationship I don’t normally lie but I want to stay over at his again but I can’t lie again but I don’t know what to tell her. If I told her the truth she wouldn’t be for it. What should I do?