Don't men like it when their wives and girlfriends are close with their friends? According to a new study that tested men between the ages of 57 and 85, erectile dysfunction is often triggered when a man's partner becomes closer to his friends than he is. The study's authors have named the phenomenon "partner betweenness," and say it could be a key factor contributing to the slump in older men's sex lives. The study found that a man whose wife or girlfriend has a better connection with his good friends is 92 percent more likely to have trouble maintaining an erection. But the issue isn't jealousy; it's about privacy and autonomy, the authors say, which are key components of a man's identity. Not surprisingly, when men enter their 70s, they're less likely to be threatened. Then the only remaining issue is just plain old science.