The hundred mile rule is a relationship agreement that permits otherwise monogamous couples to seek out other sexual or intimate experiences when they are more than 100 miles apart from each other. Another interpretation of the hundred mile rule is that it permits encounters any time one partner is more than 100 miles away from home.
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In many open relationships, couples set ground rules to protect the primary relationship, each other’s feelings and even their casual sexual partners. Choosing an encounter that’s far away from home can reduce the likelihood that sexual relationships become more intimate. It can also prevent awkward public encounters with sexual partners.