I Can Never Forgive Myself

My mom killed my first beta when I was 8 when she left for vacation and forgot about the fish, and it was during the winter so he froze to death.
A couple of years ago she took me to the pet store to get a new one, but she was focused on the price, and there was one there that was free. The employee said the beta had killed a lot of fish already and there was something off about him so everyone always brought him back. Nobody could hear my objections and I was scared of it because something about him felt evil. (I have a very close bond with animals) However, my mom also got about 10 other fish that the employees said the beta wouldn't kill.
We took them home, and I spent almost the whole rest of the day watching them closely. The beta would take turns watching me and then watching them. That night as we were sleeping, he sucked their heads and smushsed them suffocating the smaller fish, and then fought and killed the rest of them. I woke up with him having the last one in his mouth and grabbed the fish net and whacked him just enough to make him spit it out and swim away.
I got so angry and freaked out that I caught him in the net and left him out of the water for about 30 hours. When I went to check on him, he was still alive fighting and flailing in the net like a possessed snake. I quickly grabbed the net and ran to the bathroom quickly flushing the beta down the toilet. The pipes to it had been disconnected so that whatever was flushed went outside into the blazing summer sun. I knew if the heat didn't kill him then something else would.
I will never forgive myself for murdering that fish for the rest of my life. And to this day I still shake and cry from the pain, fear, and guilt of ending another living creature's life.