How do I prevent my mom from getting back with my abusive father?

I know this may not be the right place to tak about such an issue but i just dont know who to talk to.
So, I dont want to go into a lot of detail but basically, growing up my dad was abusive to my mom, siblings and me. My whole childhood I prayed and begged to god for them to get divorced. Since they would always fight and then get back, i had lost hope.
My teenage years, my siblings had left for uni and I was alone with my parents, unfortunately. I spent years begging god to protect my mom from dad’s abuse because I couldn’t protect her. Then he kind of stopped with the psychical abuse but started cheating on her. At first, I thought this was the ending point and if I told them I knew about it all, they would have to get a divorce but, ofc, they didn’t. They told me to keep it a secret, dad would stop cheating and etc. After 3 years or so, he cheated again and my mom had breakdowns from anger. She kicked him out of the house and i thought they were actually getting a divorce.
Ofc during this time he kept threatening her and I was always terrified and alert that he could harm her or even kill her. After a while he started to visit me and buy me things from time to time, which was weird bc we were almost never that close and i would feel uncomfortable around him, like a stranger. Then, they slowly started seeing each other which gave me nightmares thinking they could cancel the divorce but mom always told me not to worry and i tried to calm myself until one day he actually came back home and it was cancelled. i cried until morning and we had the worst one year. i had almost no relationship with my father whom i lived with, had a terrible one with mom since she backstabbed me. It was only after that one year, she found out that he was still cheating and she couldn’t stand him anyways, they actually got a divorce. It was again a very hard time since he kept threatening, it was a war to try to protect us from him.
after the divorce, i cut off my relationship completely with my dad for around 3 years. Now i do see him from time to time but do it mostly to get money from him, since i still feel like he is a stranger and makes me uncomfy. he does act like he cares about me and tries to be kind but, i cant trust him and even if he was sincere, i really cant help but feel almost no sympathy for him. the problem is, last year i heard that my mom sometimes gets thoughts about getting back with him, because all of us will be gone and she will be lonely. i understand her worry and don’t want her to be miserable and lonely, but i just cannot accept them together again.
Ever since i heard she has these thoughts, i started having nightmares again and worry so much. i just cant stop feeling so sad and worthless as she saw how their relationship f** me up and how many panic attacks i went through. She knows how scared i am of him. Her and my siblings think that this time the conditions are different and he may have actually changed. but i just cant accept this as he was our abuser. i worry all the things he does for me now are just to get closer to mom. she said she wouldn’t do it unless i approve but naturally, i have a hard time trusting her.
It was after their divorce that we were able to feel better and normal. I am so scared of them ruining everything again. I dont know how i can show her how badly this affects me and even if i do, whether she will care or not. What can i do to protect myself? Am i wrong or selfish for feeling this was? I don’t even know why i wrote all of this but i just feel so stuck in this thing that i am haunted by it at night.

Aren't you ashamed? How miserable do you have to be to comment something like that...?

I know this may not be the right place to tak about such an issue but i just dont know who to talk to.
So, I dont want to go into a lot of detail but basically, growing up my dad was abusive to my mom, siblings and me. My whole childhood I prayed and begged to god for them to get divorced. Since they would always fight and then get back, i had lost hope.
My teenage years, my siblings had left for uni and I was alone with my parents, unfortunately. I spent years begging god to protect my mom from dad’s abuse because I couldn’t protect her. Then he kind of stopped with the psychical abuse but started cheating on her. At first, I thought this was the ending point and if I told them I knew about it all, they would have to get a divorce but, ofc, they didn’t. They told me to keep it a secret, dad would stop cheating and etc. After 3 years or so, he cheated again and my mom had breakdowns from anger. She kicked him out of the house and i thought they were actually getting a divorce.
Ofc during this time he kept threatening her and I was always terrified and alert that he could harm her or even kill her. After a while he started to visit me and buy me things from time to time, which was weird bc we were almost never that close and i would feel uncomfortable around him, like a stranger. Then, they slowly started seeing each other which gave me nightmares thinking they could cancel the divorce but mom always told me not to worry and i tried to calm myself until one day he actually came back home and it was cancelled. i cried until morning and we had the worst one year. i had almost no relationship with my father whom i lived with, had a terrible one with mom since she backstabbed me. It was only after that one year, she found out that he was still cheating and she couldn’t stand him anyways, they actually got a divorce. It was again a very hard time since he kept threatening, it was a war to try to protect us from him.
after the divorce, i cut off my relationship completely with my dad for around 3 years. Now i do see him from time to time but do it mostly to get money from him, since i still feel like he is a stranger and makes me uncomfy. he does act like he cares about me and tries to be kind but, i cant trust him and even if he was sincere, i really cant help but feel almost no sympathy for him. the problem is, last year i heard that my mom sometimes gets thoughts about getting back with him, because all of us will be gone and she will be lonely. i understand her worry and don’t want her to be miserable and lonely, but i just cannot accept them together again.
Ever since i heard she has these thoughts, i started having nightmares again and worry so much. i just cant stop feeling so sad and worthless as she saw how their relationship f** me up and how many panic attacks i went through. She knows how scared i am of him. Her and my siblings think that this time the conditions are different and he may have actually changed. but i just cant accept this as he was our abuser. i worry all the things he does for me now are just to get closer to mom. she said she wouldn’t do it unless i approve but naturally, i have a hard time trusting her.
It was after their divorce that we were able to feel better and normal. I am so scared of them ruining everything again. I dont know how i can show her how badly this affects me and even if i do, whether she will care or not. What can i do to protect myself? Am i wrong or selfish for feeling this was? I don’t even know why i wrote all of this but i just feel so stuck in this thing that i am haunted by it at night.