Monogamy refers to the practice of having one romantic or sexual partner at one time. Monogamy can exist with or without marriage, and can be practiced by people of all sexual orientations. Monogamy is the ideal in most contemporary cultures, but other options include open relationships and polyamory.
Advantage: STD-Less
From a health perspective, one of the big advantages of monogamy is the reduced risk for contracting sexually transmitted diseases (STDs) like HIV, gonorrhea and herpes. There are ways to get STDS other than sex, such as intravenous drug use in the case of HIV. In most cases the chances of contracting one are extremely low, unless you or your partner previously had an STD. Non-monogamous people are at a higher risk for contracting STDs due to involvememtn with multiple partners and those who may or may not know or wish to share their history of STDs.
Advantage: Intimacy
Intimacy means having a deep personal connection with someone. One advantage of monogamy is that it fosters emotional intimacy, supporting two people in developing a strong, affectionate relationship. In a monogamous relationship, most people expect the search for a partner to be over, building a solid, intimate relationship that will stand the test of time.
Disadvantage: Reduced Variety
The principal disadvantage of monogamy is a lack of variety. Monogamy has the potential to lead to routine, and possibly boredom. People often equate excitement in a relationship with the ability to be with a number of individuals, potentially as part of an open or sometimes polyamorous relationship. Monogamous couples often have to work harder at variety than non-monogamous individuals.
Disadvantage: Jealousy
Jealousy can be a factor in any type of relationship, monogamous or not. Jealousy in monogamous relationship is often more a product of imagination or fear of what might happen than a reality. In non-monogamous relationships, jealousy can be a very real threat. At the same time, some individuals may choose monogamy because of a tendency to become jealous, or choose not to be monogamous because of their non-jealous nature.