My friend in high school suffered from depression in part because he was well aware of that fact that his parents were only staying together until he graduated. Despite any attempt to put a rational face on it, he believed his existence was the source of his parents' unhappiness.
Another friend of mine is doing this with his wife right now. He's utterly miserable, but the racial stereotype of the missing black father weighs so heavily in his mind that he's resigned to just counting down the years (despite my own attempt to convey the above story).
I think that staying together for the kids is essential for the very early age, but if someone goes it must be the dad. My mum left when I was 1 and a half and that is obviously horrifically painful
At a certain age though the parents should split if it isn't working. It's definitely far easier to deal with your dad or mum leaving if you're 10 years old than if you're 1 year old
Another friend of mine is doing this with his wife right now. He's utterly miserable, but the racial stereotype of the missing black father weighs so heavily in his mind that he's resigned to just counting down the years (despite my own attempt to convey the above story).