When it comes to kids, there's a lot to consider. Attachment to a mother is the most important thing in a child's life. Even if it's a bad attachment, there may still be some good there of which you're not aware, and that bit of good can be better than no attachment at all. If the child is taken away, there's a possibility that it will end up in an even worse situation, such as with other predatory family members, or a predatory foster family. Therefore I caution playing God in such a situation, as the child could be given better opportunities, but could also be destroyed. It doesn't seem that your focus is on what's good for the child, but on the destruction of its mother, and the child has only become a focus in order to validate an act of revenge so that you can feel just in doing so. I caution that you are making the child a pawn in the strategy of your game. How are you any better than the mother? Because it seems that you are acting in self-righteous indignation and want to see yourself as better than her, since your partner's cheating with her made her seem better than you to your partner. Your beef is with him, and maybe with yourself, if you're prone to blaming yourself for your mistakes but can't deal with that, so blame must be directed elsewhere to discharge your pain and discomfort, followed by condemnation, judgment, and punishment.
Whatever power you lost by your partner cheating with her, you're not going to become more powerful by being the vengeful God in her life. If she was indeed destructive to you, and you respond by being destructive to her, I wonder: Are you then better than her? Are you then as bad as her? Are you then even worse than her because you are intentionally targeting her, while you were not the primary focus of her unwise action in hooking up with your partner? He chose to step out, and she was available and willing; if not her, it would have been someone else.
The only thing you can potentially control and which therefore gives you power is your own life. You can ditch the partner you hate. You can move forward without him and good riddance, you are free from life with him in it and all the shit that goes along with his presence, and you gain more power over yourself and your well-being. You can choose to end your life, with dignity and self-respect, because that's 100 percent about you, done only to you, and focused on you, and you become free from life all the shit that goes along with it if there is no value in life and nothing in your power to strive for.
Focusing on everyone else gives them power over you and directs your actions; focusing on yourself is self-empowering and also directs your actions. In my experience, the latter is far more rewarding.
You can keep hating everyone else, or you can start working toward respecting yourself and treating yourself as you want to be treated, since you are the one you have to live with whether you want to or not. You are also the only one you will die with; you won't be dragging anyone else along with you, much as you might like to. So where do you want to direct your awesome power? And how do you want to wield it? Toward the ultimate destruction of others and yourself, or toward becoming your own foundation and building from it?
