Divorced parents

I need some advice. So my parents got divorced 10 years ago. I was young but I still remember the emotional toll it had and still has on me. My parents are really close though still, but sometimes they fight, bad. Today they did but apparently over text message. My mom left my dad and my siblings and I because she cheated. Like I mentioned I didnt really know the whole story back then. I remember being really worried because I didn’t know where my mom was and I couldn’t call or text her because I didn’t have a phone. My mom got out of a bad emotional abuse relationship like 3 years ago. Recently he apologized for everything and has “changed”. My mom has been going to his house on the weekends and my dad has gotten really mad because she hasn’t been home she’s been with her old boyfriend. He keeps bringing this up to her saying she should be home not out with him. Apparently my dad and mom got into a pretty heated fight like mentioned over text. My dad seems to not be able to get over her cheating on him even though it was so long ago and they both have had other partners. I think he’s really upset though from how she left us kids with no valid reason to us. So we were left in the dark. Anyways this really hurts me when they fight because I feel like I have to choose a side. My siblings choose sides a lot but I’m not like that. I feel like I should be mad at my mom but I know my dad has said rude stuff to her. Anyways I really need some advice on what to do. And how to fix this mess.