I was struck by a recent study showing that people might be more likely to cheat on a partner in the year before a milestone birthday. This suggests that if you’re in a committed relationship, you’re at roughly a 10-year cycle for heightened risk of infidelity.

Researchers said they worked with Ashley Madison, a dating website for people seeking extramarital affairs, to analyze data on more than 8 million men who had registered with the site. The study was one of six published together in the journal “Proceedings of the National...