I'm really ready to begin going in a different direction now. The letter and the chat to my in laws this weekend is that last I can do.
Liam -
I feel for you. I know this situation is pretty bad.
My advice is to stop involving yourself with the inlaws so heavily. There is no reason you should know the details of her interactions with them or their detailed feelings. Let it go for now and focus on whats important. Speaking of which, PLEASE DONT send that letter. You say that the contents include "my opinion on her actions and how it will effect our kids and her own future." I am certain that she does not care about your opinion one little bit.
I get that you feel like you need to do 'something'.
Remember that choosing to do nothing IS doing something. And often times, it is an incredibly STRONG action.
