Creating a safe place for almost 17 year old to have sex

I feel like I'm going to be judged so this a lot but I do want opinions. Just plz keep them nice. If anyone saw my post over the past year me and my husband fostered and then adopted a teenage boy. I was super hesitant about keeping him because he attempted to burn his last foster families home down but that was because the dad and the other foster brothers abused him sexually while the mom starved and physically abused him and he was sodomized by them all in a basement. He is a really sweet kid and has his trauma that we are working through. So he is turning 17 in October and he is gay and has someone he says he's just friends with but we've seen them kiss and he's come home with a hickie. He said they haven't had sex yet. This "friend" is spending the night this weekend and I know our son sees home as a safe place. He has problems with accidents at night but feels more comfortable about it when he has sleepovers here instead of at others homes. So me and my husband feel like we need to speak to him about sex. It's just been hard to find the right words because he's been severely sexually abused and we both agree that if he's gonna have sex.... We want it to be under our roof where he is safe and not somewhere sketchy. I know a lot of parents disagree and obviously we don't WANT him having sex but teens will have sex and we know that. We just want him to know home is a safe place all the way around. If they were to have sex at the sleepover while I wouldn't be thrilled I would at least know of he if things became dangerous or unconsensual he would call for us. And that's not us saying we want him to only have sex when we are hear. I'm trying so hard to explain this without sounding like a creep. My point is, especially with his trauma we want him to know if he's going to have sex he wouldn't get in trouble for it being in the house because this is his home, his safe place. He should feel safe hear, whether if it's safety from nightmares or safety to have sex.