Wrong or nah? (Sorry it's long)

Okay so, it's my boyfriend's formal in about a week. And I've asked my mum if I can sleep over his house afterwards. It was a straight out no. Not that I expected any different given that my mum is quite strict. But she started saying things like she can't believe I think it's even okay to think about sleeping over his house. Now, I've been dating him for about a year now (we haven't had sex) and he's the most respectful guy I've ever known and we've spoken about if we were to have sex and if it happens we're ready and whatnot. But mum doesn't know this, she was condemning the idea of me even wanting to sleep over. She doesn't understand that it's not abnormal in this day and age. I get why she's worried but I honestly just want to know if it's so wrong that I wish to sleep over his house? I've just turned 18 btw.