Classic Monogamy:
Classic monogamy is a relationship between two people who marry as virgins, remain sexually exclusive their entire lives, and become celibate upon the death of the partner.
Serial Monogamy
Serial Monogamy is the cycle in which people are sexually exclusive with each other for a period of time, break up, and then re-partner in another sexually exclusive relationship with a different person.
Non-monogamous
Non-monogamous relationship, are diverse and vary by degrees of honesty, sexual openness, importance of rules/structure, and emotional connection.
Cheating
Some people see a non-monogamous relationship as adulterous, regardless of whether or not both partners have consented to having sexual interactions outside the committed couple. But transparency matters, and consensual non-monogamy is qualitatively different from non-consensual non-monogamy, or cheating. The two relationship categories also have distinctly different outcomes for the people involved: Not only do consensual non-monogamists try to tell each other the truth, but this greater communication has real impacts, such as smaller rates of STI transmission among consensual non-monogamists than among non-consensual non-monogamists. Many non-monogamists rely on honest communication to negotiate consensual agreements that allow a variety of ways to have multiple partners.
Even though contemporary society agrees that cheating is undesirable, people still do it! It is estimated that 20-40% of people cheat at some point in their relationship. Defining cheating can be quite difficult, because it may include a wide variety of behaviours that are not directly physical sex, from sending virtual flowers to video chatting on Skype to a “chaste” lunch date with no physical contact, but an emotionally intimate conversation fraught with repressed passion, to paid phone sex with a professional.
Open relationships are varied enough to be an umbrella term for consensually nonmonogamies relationships based on a primary couple who are “open” to sexual contact with others. The most common form of open relationship is that of a married or long-term committed couple that takes on a third (or sometimes fourth or fifth) partner whose involvement and role in the relationship is always secondary. A couple practicing this relationship type might engage in sexual activity with the secondary partner together or separately, or they may each have independent outside relationships with different secondary partners—regardless of the specific parameters, the primary couple always remains a priority. Generally rooted in specific rules, expectations, and communication between those involved, open relationships may take a variety of forms and may evolve over time as needed to meet the needs of those persons involved. Swinging, monogamish, polyamorous /polyfidelitous, and anarchistic relationships can all be considered “open.”
Swinging
Among recognized or intentional forms of non-monogamy, swinging is the best known and most popular. Most broadly, swinging involves committed couples consensually exchanging partners specifically for sexual purposes. It is tremendously diverse, ranging from brief interactions between or among strangers at sex parties or clubs, to groups of friends who know each other and have socialized for many years.
Monogamish
Monogamish are those in which a couple is primarily monogamous, but allows varying degrees of sexual contact with others. As with other non-monogamous relationships, rules structuring these external sexual contacts vary by couple: Some allow only one-night stands or only specific kinds of sexual activity (kissing and groping are OK, but no intercourse), and others have time or location limitations (no more than a week, or only when people are traveling or not at home).
Polyamory and Polyfidelity
Polyamory is a relationship style that allows people to openly conduct multiple sexual and/or romantic relationships simultaneously, with the knowledge and consent of all involved in or affected by the relationships. Polyfidelity is similar, except that it is a closed relationship style that requires sexual and emotional fidelity to an intimate group that is larger than two. Polyaffective relationships are emotionally intimate, non-sexual connections among people connected by a polyamorous relationship, such as two heterosexual men who are both in sexual relationships with the same women and have cospousal or brother-like relationships with each other.