I housed a teen for a while and my rules were anything had to be safe and with positive consent. I knew banning sex under my roof was a fools errand.
I also gave permission to use me as "the bad guy". That if they ever were unsure and wanted an excuse, they could say, "ugh, Vanth makes me keep the door open. Lame adult, amiright?" They used that at least once that I know of.
They're an awesome adult now who is far better at having healthy relationships than I was at that age.