This research found that divorce can spread between friends, siblings, and coworkers. It also extends to two degrees of separation. The process it like this: A divorcing person confides in a married friend. That married friend may not decide to split with his spouse, but tells details of the conversation about the divorce to a third party, influencing that third person to get a divorce.
Scary, but real stuff. The research was supported by the National Institute on Aging. Read the whole study here