419, I hear ya. Like I said, I had friends whose kids lost their dads when they left and the kids were about that age. And one friend's kid it was super easy on. The dad was not involved at all. So when the parents split up, the kid didn't notice the dad gone. The dad is actually a better dad now that he's only part time. But my other friend, the dad was really involved. But then split one day. And it's been years later and it's still traumatic on the kid. The dad is bipolar, so I think the fact he's so unstable is what makes it so hard on the kid. Which is what we'd all be dealing with if we left our spouses, unstable exes. 

Unfortunately, it's hard to know if a house with a unstable parent, or a house without it but losing their parents in the same house, is worse. There's no real easy answer. Even those friends who got divorced. It was the unstable parent that left. Not the nice one who put up with the drama. So my friends just had to make the best of what happened after that. But even they probably never would have chosen the divorce. That's why it's hard. We are the rational cognitive partner, and we are aware what we could or could not be doing to our kids.