There are reasons to be fair. If you value your children's wellbeing over your own then there is an argument to stay together (when possible) because generally kids raised by both their mother and father will do better for it.

Although to be fair to you this doesn't apply in the case of Bill and Melinda as all their kids are fully grown.

In general though I think people really should try hard to make relationships work. Our culture today seems to down play the importance of long-lasting relationships, but there is so much value in having someone who knows you better than you know yourself and who you can trust to always be there for you no matter what. A lot of people (or at least my friends) in relationships today don't seem to want to put in the effort to get to know someone on that level. Even in relationships they seem to be emotionally alone and empty in a lot of ways. I don't know anything about Bill and Melinda's relationship but they seemed to share a very close connection. Perhaps this is for the best, I don't know the situation, but I do worry neither of them will find that depth of connection again.