Are Breakups Contagious?

In the Guardian's "Private Lives" column today, a reader writes that she broke up with her boyfriend of seven years because two days before they were closing on the sale of a house, he told her he was worried about commitment. She said it had to be all or nothing; he chose nothing. Now, a couple the reader and her ex are friends with are also having problems: After being together for twenty years and planning summer nuptials, the man is suddenly not sure about marriage. The reader worries that her ex influenced the man. Here's the question: Are breakups contagious?

One commenter on the Guardian's site responds to the dilemma with the statement, "You are not responsible for the decisions that other people make." Yet another opines, "I do not believe that your ex could persuade him to call off his wedding. The man must have had his own doubts about marrying your friend before your relationship broke down." But expert Linda Blair writes:

It is likely that your ex did influence this man - they are good friends, so no doubt they value one another's opinions. But I don't see why this should matter to you. You are not responsible for your ex's behaviour, nor for that of his friends.
What's the deal with the relationship-domino effect? If everything around you crumbles, are are you more likely to fall? Could being close to a couple who splits make your relationship suffer? And if so, is it fair to blame them?

Has My Ex Helped To Split Up Our Friends? [Guardian]