I'm really bothered that my teenage son is living with a female so soon. Any advice?

Hey guys I need advice. My son got emancipated in December and he's still getting his apartment set up. What I did not know is that there's a "girl" (Older woman!) living with him. He doesn't speak to me about his personal life and it's really sad that I didn't know about her. She's 20 and I got no clue how long they've been seeing each other. I just want to communicate with him that I don't think moving in with the opposite sex at 17 is smart. At that age he will be very impulsive and if living alone without parental supervision, I know what's gonna go down. One mistake can lead to a baby or STD or anything like that. Also if they break up what would he do? I'm just really bothered by this.