had a talk with her then with them both together seems ok no sex.if he has sex with her he is breaking the law.all seems ok a bit of respect both ways?
Honestly, they are going to be sexually active. It would be better for you to acknowledge this and ensure that they have access to condoms and a safe environment to have sex. I saw it too many times where parents forbid their kids from having sex and the kids ended up doing it in bushes/bathrooms or other places, not practicing safe sex and having no one to talk to about it.
My parents provided condoms in the bathroom, and were very much of the view that if I wanted to talk to them then I could and I wouldn't be in any trouble and no judgement would be made. This is a much healthier approach than trying to forbid them from doing anything.