Friends boyfriend has STD and she won’t listen to me...

My friend just started dating this guy. He dated my best friend a couple years back and he is a MAJOR man whore. I KNOW that he has an STD because he gave it to my best friend. I tried to tell my friend that he has one and what a scum bag he is, but she will not listen to me. She say’s she doesn’t believe me and that I am just jealous of them. Keep in mind that I am happily married and have been for 2 years. I am just trying to look out for her and give her a heads up and because he is lying to her, I come out looking like the bad guy. I mean I guess she will find out eventually. I just hate that she is going to have to find out the hard way. She has already had a really hard life.

*Added*

The STD is HPV. He still has it.