I am so sorry. I know it's terrible right now, but you've got to pull yourself up and realize that you are the lucky one. You have your head on straight, you are acting like a responsible adult, your moral compass is pointing in the right direction. And, you have your dear child. You don't deserve this treatment, no-- no one does. But there it is. I know it hurts. But try not to focus on it. The two of them are horrible idiots, it's true. Let them be in their fool's paradise. You've got the good stuff, and what they have is like a house made of a deck of cards.
I am reading a book right now and last night I read a line in it about: Don't allow yourself to fall apart if you can help it, because then it becomes a habit. This really struck me!
I think the most important thing you can do right now is get reconnecting with any and all support systems. You need to talk, you need to be heard. Do you have a therapist? Can you call your old friends and let them know you really need them right now? Once you get past this crisis time, then it's time to meet new friends and support so that you have a full life and plenty of support.
You're not alone, ever. We are here. There are so many, many people in your same situation. Even if you are physically alone at times, remember that you are not alone in the universe.