This is the most important lesson that you need to get out of this situation, kech.
Kech has control of kech. Not Kech's H. Not his OW. You know that controlling him will not work. But you do know that you can control yourself.
I agree, D is scary. I myself have not fully embraced it yet. I know it's a definite possibility. But I also want to be happy and share my life and love with my partner. I will not be stuck in limbo and accept things "as is" just to keep the peace.
You are a wonderful, strong, smart, caring, beautiful person. And you want what is best. Right now, you want what is best for you and your daughter. It will be H's loss if/when you move on.