Scard of someone in the family ? how to live w/ this?

im scared of my moms husband , and dont know how to handle this anymore , especially now that im having a baby. he used to beat up my mom when i lived w them and he kinda abused me bec. he used to watch me and check me out in a sik way and drive by my school, but mom never believed this she said that im crazy and he can find someone so much better than me. Im scard of this guy meeting my baby and even just being around my baby but dont know how to handle the situation since i want my mom to b part of this.