Thank you for all the replies. I did tell him that we would no longer be having sex and def no oral sex unless he started using condoms.
He then responded by saying I was putting him in a bind by making him choose her or me even though he would continue to use condoms with me (so I'm not sure how I'm making him choose). He then asked if I would consider seeing him in just a D/s capacity without the sex.
This of course broke my heart, makes me feel like our sex life is nothing to him.
I've been with him for over a year now and yes it is hard to walk away from that. He said he knew she was clean and I was not at risk for anything.