"Thinking about adding something like this to the letter, but not sure where to fit it in:
I've tried to figure out what I did to you that was deserving of these lies and this nightmare in general, but have come to accept that maybe it is something I will never understand.
Too much blame? "
I can't tell if you are being serious or not. Assuming you are, yes, it is too much blame.
You are still trying to work out problems in your old M. Your old M does not exist. Both you and H will have to work through those problems in a new R, whether it is with each other or with OPs. But, those problems will be addressed in the context of an R between romantic partners. You are not romantic partners now. There is no current need for you to address such problems.
Try journaling. Get a journal and write letter after unsent letter to H. But don't send them. It is not appropriate. It is not going to help you reconcile. It is not going to help you move on. It is not going to help you be better co-parents. Let the old M go and focus on yourself.
