Should I just let it slide or stand firm with my moral beliefs, even if it cost me my marriage?

I am a stepmother of a 17 yr. old female/lesbian. She is a daddy's girl and he allows her to sleep with her partner in our home. My opinion/beliefs on the situation is well known.I was told I have no say in the matter. Dads main comment is, at least she cannot get pregnant. Hello STD. I have 3 children myself the youngest 17 also, and I never knowingly let them sleep in my home with their signifigant other. Feel disrespected.