The model for romance in our culture is so dominated by the monogamous male-female relationship that most people subscribe to it without stopping to consider the alternatives. But not everyone is uncomfortable with sharing his or her partner.
People in open relationships often feel joy or pleasure when their partner has romantic adventures with other people. This feeling is sometimes called compersion. The Keristan Commune, a now defunct San Francisco-based polyamourous community, gets credit for coining the term, which is often defined as the opposite of jealousy.