Having not read all your thread , i am not sure if this has been covered but i also believe that as well as age approriate truth, kids need to see the emotional fallout.
If you try to be strong and tough, you run the risk, that they think this sepersting/ divorcing as easy and okay. They could also accuse you as not caring.
I have seen this happen to a friend. Her H left her for anothe rwoman. She kept it together for the kids... and as adults when the converstaion turned towards what Dad did years later, they were shocked at the pain and suffering of their mother and that they had alwayd believed their mother had not really loved their father ( hence the not caring , when he left ) and it sort of justified their Dads behaviour.
To me Dad got a ' get out of jail free ' card.
So when my H finally left and i was devastated , my kids knew to a point on how hurt i was. They saw the pain and they saw the survival. Perhaps the only up side for children of divorce is that they learn that there is survival when adversity strikes in your life.