Dude you have to detach. YOU are letting her control your emotions. I'm going to attribute this to you and your W being fairly young because that's how both of you are acting. Like kids.
It doesn't matter what she's doing, who she's doing, etc. Because YOU CAN'T STOP IT! What you can stop is how it affects you. You were doing well with the detaching until you found out about the OM who is in the same mental maturity level as your W. The reason being that it is all she can handle right now.
Concentrate on yourself and the kids. Go back to NC unless necessary. Instead of venting about taking the car back, do it. It is your car after all. Protect your assets. You did the right thing in telling her she needs to buy her own clothes for the kids. Do not make it easy for her.
If she continues to pawn the kids off to you, then file for primary custody of the kids. It will be tough and a hardship for you, but she's not going to make things any easier on you.
DO NOT contact her. DO NOT open your mouth. Let's face it, every time you do, the same thing happens. Yet you sound amazed eveytime it does. Stop the cycle and see how things go.
Like a child, once she finds out that she can't get a reaction out of you by pouting or screaming, she's going to have to look to herself to solve her problems. Take the target off your back. Think of her as a child throwing a tantrum until she gets what she wants. What do adults do in a case like that? They ignore the kid and let it run it's course.
You can do it. Show her who the one is with the REAL maturity.
M-43 W-40 2D - 9 and 5
Emotion, yet peace. Ignorance, yet knowledge. Passion, yet serenity. Chaos, yet harmony. Death, yet a new life.