I'd tell my dd she needs to be on the pill and insist on a condom to prevent pregnancy and infection. Then she is in control of her own body.
But what worries me is this
Me - Son, you need to make sure you wear a condom so your new GF doesn't get pregnant and so you don't get any STIs.
DS - But we won't get any STIs, neither of us have ever been with anyone else and she's been to the docs to get the pill.
Me - Yes, I can see how you think that will protect you from becoming a Dad at 17, but it might not.
DS - Why not Mum? I know I've never had sex with anyone else so I can't give her an STI, and she tells me that she has never had sex with anyone else so she won't have an STI, and she said she knows that she has to take the pill correctly.
Me - What if she forgets to take a pill?
DS - Come on Mum, she's not stupid, she's just got As on her A levels!
What else is there left for me to say that will convince him that he really does need to wear a condom if I don't point out that she could be taking the pill wrong, or lying about taking the pill at all, or lying about having had sex before?
I can't imagine my future teenage sons taking my word as gospel on everything, so I have to say something that sounds convincing! Especially when he would probably prefer to believe that the pill is being uses effectively, because lets face it, condoms are bloody horrible!