Dear Economist: Should I marry my boyfriend?

I have a great boyfriend. We’ve been together for five years, have a son and are planning more kids. I have a good job which I would like to continue doing and that pays OK. My boyfriend earns a lot more money than me and we have a very comfortable lifestyle. We are both in our early thirties but I am worried that after three kids and 10 years with me, he’ll run off with a younger woman. Should I marry him?

C.M., France

Dear C.M.,

Economists have gathered evidence from speed dating and internet dating, and found that it supports the conventional wisdom: men like young women and women like rich men. Clearly, you have reason to be nervous.

I keep re-reading your letter and I cannot work out whether you regard the risk of desertion as a reason to get married or a reason not to. No matter: a spot of game theory, which economists use to understand how rational people interact with each other, may help you here. You have three options: dump him now; stay with him but do not get married; or get married now. Ten years later he will respond by staying with you or leaving you for the nanny.

Dumping him seems odd: you already have a child together, you enjoy the relationship, and dumping him will not change the unpleasant logic of evolutionary psychology, which puts you at an increasing disadvantage as you both grow older. Staying with him seems more sensible, but if he does run off you will have limited negotiating power. Marrying him seems best of all: the legal contract, in most jurisdictions, protects you against this sort of behaviour. You cannot prevent him leaving you, but you can make it an expensive proposition for him if it happens.

Do I hear the distant sound of wedding bells? Happy Valentine’s Day.

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Tim, also known as the Undercover Economist, writes about the economics of everyday life.