People who are nosey and fake

So my work group for my college has these 3 girls in it. At first they were nice and we were friends but then I realized how fake/mean and how much they lie. Well they are fake because we have breaks and they only text me to ask if my bf and I have had sex. They made fun of me and called me really inappropriate names. They hurt my feelings and have said stuff in front of my bf which I don't appreciate. 1. I'm a private person so regardless wouldn't tell them 2. They aren't real friends so why do I care. I am stuck being with them until January and wondering should I lie and say yes and say it was last year