My oldest brother divorced his second wife, and they went out of their way to stay civil, because they had joint custody of their kid.It is different if two people just decide to divorce, or one says I want out, but nobody else is involved. I could still be friends under that kind of circumstance. But, when there is a third person involved, it's just too weird to stay friends.
CD
He remarried...she remarried. All that was nearly 20 years ago, and now, the four of them are best friends and (until recently) would hang out together, in and out of each other's houses, etc. People who don't know them are surprised to find out that two of the four were married at one point.