I dont understand my dad help?

My ndad the worst person in existence. He was originally a good person but when I turned 13 he became super abusive. He has replaced us with kids and wife that are similar ages to us but better. He hasn't contacted me and my brothers for years, just harassing my mom. But earlier this year my grandma found a box with all of our childhood scrapbooks intact with no defacing or anything on her front door. My grandma has lived in the same house for more than 50 years. My father told my mom he'd throw them out since they're useless to him. I also checked his Facebook because theres an ongoing case between my mom and dad. But he hasn't deleted any of our photos. Saying that we're his kids, nothing about being proud. But when we were a semi-functioning family. Ive already come to terms that hes a horrible person that deserves to rot and that he threw us away. But now Im just confused and hurt hurt. Like why would he put us through such horrible things which my therapist compared to treatment of a POW. Im so confused, upset, angry, hurt. Has anyone else experienced something like this?