I like all the ideas posted here, but each situation is a case by case basis.
There are divorces where two people dont get along and they cant put their finger on how they drifted apart after at one point in life they could not get enough of another.
There are divorces where the two people are nice as individuals, but horrible to each other in the marriage.
There are other cases where someone IS to blame, and at fault. They did wrong. And the wrong they did, or continued to do, is not easily, or cannot be repaired, and they create sorrow and need to ask for mechila.
The idea that these tragic situations were 50/50 in responsiblity, is not always correct or a just way to view a given situation.