My family is falling apart

I’m not sure if this is the right place to post this but I just need help/ just to talk about this. I am 20 years old and I live with my fiancée. I’ve been moved out of my parents home for over a year now. Growing up my parents did argue a lot. It was usually about money. Me and my younger sister (who is 15 now) didn’t like all the arguing but we by no means thought our childhoods were bad. Our parents still showed they loved each other despite the bickering and made time for each other. But now my parents have been together for almost 30 years and they are going through a very tough time. It seems like as soon as I moved out my family began to crumble. My mom and dad began to argue more and more. It came to a head last summer when they got into a argument and my mom smacked my dad and he grabbed her by the arm and threw her outside. The police were called (we still don’t know who by. Think it was a neighbor) and my dad was arrested and had to be put in anger management courses. Ever since then it has been a living hell for me. My mom stays out all the time. She’s been gone for 4/5 days at a time and she takes my sister with her. She usually stays at my aunts but has been known to disappear without letting anyone know where’s she at. My dad has become obsessive. He calls her constantly and she never answers so he calls me wondering where she’s at. My mom calls me a lot too to complain about him. I definitely feel as though I am stuck in the middle of this and they want me to pick sides. My younger sister has picked a side—my moms. She rarely speaks to my dad. I just can’t do that. I love them both dearly and they have both done things wrong so I refuse to take sides. Recently my younger sister confided in me that she saw a questionable text message on my moms phone. It was from our uncle( my moms brother in law) and it was talking about how he was horny and she need to fix that. It literally made me sick. My sister confronted my mom and she denied everything. I don’t have the heart to tell my father and plus I’m afraid he’ll lose it if I do. So last night my mom apparently told my dad she is leaving and taking my sister to find another place. My dad is devastated. Although they fight a lot he does really love her and she is the only women he has ever been with. He called me to tell me and it was the first time I have ever heard my father cry. My dad is not happy being alone and has asked me and my fiancé to move in with him so he has someone. I wouldn’t mind but I know it would be hard. He is in a very tough place but at the same time I don’t want my mom to feel like I’m picking sides. I love her just as much as him and it’s killing me to be put in this position. I also worry about my fathers mental health. Since this all began he has made “jokes” about running away and even killing himself. He told me yesterday everything he has done was for us and now that that is gone he has no point in living. Please any advice or comments would help. And please no rude or mean comments about my parents. Like I said I believe to some extant they are both at fault but they are still my parents. I just want my family back :(