Mom's new boyfriend

❤ Stephanie • Just a small town girl trying to make a living. Currently in a long-term relationship with the greatest guy ever!
My mom started dating this guy, well call him Steve, and I honestly do not like him. He told my 14, almost 15 year old sister about his sex life with my mom. And not only is it inappropriate to do, he went into details. My mom thought it was hilarious that he was telling her this. Baby Girl told me she thought it was gross and asked him to stop talking but he kept going on about it. Also I have another little sister, who is 18, almost 19, who claims he told her the samething. He hasn't said anything to me about it, mostly because he knows I don't like him, and unlike my sisters I can be a major bitch. I have decided that next time I see him, I will tell him exactly what I think of him. And although me and my mom do NOT get alone I'm sure this will piss her off, but oh well. You do NOT tell a 15 year old kid about your sex life with her mother. He's an inappropriate, perverted, drunk, and I do not care for him at ALL!! Should I say something to him, or talk to my mom about it first?