It sounds like she's having personal issues and you are getting walked all over for it. Set boundaries. When my bf uses a tone with me I don't like or I feel I am being attacked for some unknown reason, I call them on it: Why are you talking to me like that? Why are you attacking me, I just said _______?

When she says I try, ask her how. When she gets upset, let her rage and when she's finished continue the conversation. She's used to you backing down. That's why I suggested you send the kiddo away and spend and entire evening talking about it. Don't let her get away until your points are made and there is some kind of agreement. If she refuses to admit anything, go to counselling, or seek help in some way. Suggest a trial separation for a month or two weeks.

Sometimes when we get stuck in a situation we really can't see what we are losing or what we are or are not doing.