What is it that you want? You talk about how badly you are treated by your W and BIL. How you are not appreciated or respected in your home.......and how it makes you angry when your W bullies you.
What do you mean you are quite happy acting like a single parent? You aren't acting single anything. You spent Saturday with the W, doing things as a family.
So again, what is it that you want? If you just want the fighting to end, then you may need to attend anger management. It doesn't necessarily take care of the other disrespect you receive at home, but it may teach you how to handle your own anger issues.
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!