WTBH, I'm hurting for you today, for what this guy did to you and for how your mom helped him do it.
I'm still entangled with my abusive ex on custody and child-rearing issues in part because I never reported him to any authorities -- I listened to my mother, who told me to think of my son and let it go, be the bigger person, refuse to escalate. But it escalated, and in not reporting it I gave him power over me he has used to run my life through joint custody "agreement". If I could go back, I would have reported him. Every. Time. He pulled the same things on me -- the gaslighting, flat-out denial of hitting me or stealing money, etc -- and the one, single, solitary report that's out there is from the time I lost control after yet another one of his antics and slapped him across the face. It left a scratch mark and he called the sheriff on me.
If you can get away from this guy, run. Don't listen to your mom. Don't second-guess yourself. I'm praying you don't make the same mistakes I did and find yourself raising your child WITH your abuser, and watching him do the same number on your kids' heads that he did on you. Please don't be afraid to protect yourself. You deserve it, your kids deserve it, and it's your RIGHT to be safe from him.
What's the atheist version of prayer? Because that's what I'm doing right now for you and your girls. xxoo