Earlier this year, while talking to a married couple about how their sex life was going, the wife brought up something that, believe it or not, I’ve been asked several times before: “I don’t know if it’s all in my head or not but there are times when [my husband] devours me and then there are times when he is less enthused.” When I waited for the husband to confirm or deny, at first, it took him a second: “I’m always going in. Sometimes I’m confused because it tastes different...