DD15 met a girl the same age but from a different school a couple of months ago at sixth form college open day and they immediately hit it off. They have been hanging out a lot and DD has stayed over a few times. (I've met her mum and she is lovely). They have now decided to start dating. I think now they are dating she shouldn't stay over. DH doesn't care as "it's not like anyone is in danger of getting pregnant."
For context she has a twin brother who has been with his girlfriend 6 months. We have previously discussed that are not allowed to sleepover at each other's houses (not that they've asked) and that we would revisit the conversation once they are both 16.
DD told me a couple of years ago that she is gay but this is her first relationship.
YANBU - Sleepovers are no longer appropriate and consistency with DS is important.
YABU - Let her sleepover, she was allowed to before and changing the rules now just makes it weird.