1) the sexually exclusive couple (monogamous);
2) the sexually non-exclusive but unacknowledged couple ("cheating");
3) the primarily sexually exclusive couple, also known as "modified monogamy" (those that perhaps participate in occasional three-ways or group sex together);
4) the sexually non-exclusive acknowledged couple (the open relationship), and
5) non-sexual domestic partners. He describes how for some couples, "fidelity" is defined by the emotional primacy of the relationship, and abiding by whatever rules the couple has agreed upon for how sex outside the relationship should manifest; while "infidelity" means not sex outside the relationship, but breaking the set rules, such as engaging in unprotected sex outside the relationship when it was agreed condoms would be used, or having sex locally when it was agreed they would play with others only while traveling.