Here's some common reasons for divorce:
Abusive behaviour (towards spouse/children; can be physical, verbal or sexual)
Active addiction to alcohol
Different expectations about rearing or having children
Untimely death of a child
Lack of communication
Not able to resolve conflicts
Active addiction to drugs (including child drug abuse)
Different expectations about housework
Developing a cyber-sexual-relationship on an internet chat site
Developing a sexual relationship with another person (extra marital affairs)
Financial difficulties
Imprisonment or criminal behaviour
Intellectual incompatibility
Use of pornography
Whilst being business partners may not be the root cause of the divorce, it may result in partners not having the space to resolve underlying problems.
Some people think a reason not to get divorced is being too old (many disagree).