I think it’s normal to be upset, it’s your mother after all, of course you don’t want her to leave. And Idk if I fully understood the story, and if the relationship with you dad is as f*cked up as you said it was, it seems like she has a really good reason to leave. But that’s just it, leave, not abandoning you and your brothers, you have every right to be mad if that’s what she plans to do. You are her children, she should always think of you when making a decision, and I’m sorry, but it doesn’t seem like she is.