Court issues with petty baby daddy

Daughters dad has moved his new girlfriend of 2 weeks into his house didn’t tell me she’s been around our daughter. She denies dating him he says they do. She posts about their sex life but also has pictures of her drunk at 9am and smoking weed. I asked him about this and messaged her directly both cussed me out and told me I will be losing full custody of my daughter for snooping. Is this true. I live in South Carolina if that matters