I generally feel better off without the ex, but every now and again there is the thought, "What if I had taken her back when I had the chance?" I mean she is a pretty horrid person, but I wouldn't have been with her if there wasn't something good about her.
i really believe humans just aren't made to live monogamic or to stay in lifelong relationships. society decides what is deemed normal and healthy which leads to all kinds toxic relationships because people suppress themselves to function how they are supposed to. sure if you have a kid it makes sense to stay together, but most marriages are basically over by the time kids leave the house and already more of a functional relationship. you share the life and goods and responsibilities but you're not about the other person anymore. it's like building a house, once it's done, even if it is flawed, you want to live in it if you build it yourself, saying to yourself "it's not that bad actually, also i can fix this!" even if half of it is covered in mold and shit.
i'm sorry to be this frank, but wishing to be again with a person you describe as horrid just now is a very unhealthy thing to think. you should strive for a good life solo. having a steady partner is cool, but it's also overrated. if you can find happiness and content in staying alone, you've done more good to yourself than many unhappy couples. and then you can go from there to find a partner that has similar strength and build a true synergy instead of mutual dependencies.
stop the active dating thing and just let things happen or focus on how you can improve your life without another person. there is nothing more unsexy than a person that comes off unindependent and devout to the point where you can be an asshole to that person and that person will stay no matter what because their whole selfworth depends on being in a relationship with someone, even a total asshole, and you sound like that devout person rn.
you did the right thing in not taking your horrid ex back.