I really want to stay over!!

Ok basically I’ve been casually seeing this guy. Buy that I mean we slept together 3, and talked for almost 2 months. I’m 20 and his 25. We both live with our parents it’s no big deal because where I live in Australia it’s common also I don’t pay rent. Anywayyy I really want to spend the night at his, he has told me I can. But I don’t know what to say to my mum I’ve never slept at a guys place even when I was with my boyf. When I was with him I asked and it was fine if I went to his but not for him to come to mine I understand that. But what can I say to her this time because she doesn’t know the guy. I know it’s weird that I have to “ask” but my mum and I have a really good relationship and she knows most things that go on but I really don’t want to lie to her and I feel a bit awkward asking because she will know it has to do with sex.

Btw I’m on the pill so it will be protected