Ben Smith* has been with the same woman for 13 years. Every third or fourth time he has sex with her, another woman is present in the bedroom. For all he knows, his partner has no idea.
They’ve never discussed fantasizing about other people during the act, and Smith rarely did in the early years of their relationship. But ever since they hit the five-year mark, imagining he’s having sex with other women mid-climax has become a “semi-regular occurrence,” whether it’s a porn star splayed out naked on the edge of the bed or that woman he interviewed for a job last week.