Brian D. Earp in New Humanist:
For many generations in societies shaped by Christianity, monogamy has been the almost undisputed champion of relationship norms. In Britain and the US, it has been held up as the dominant – really the only – ideal for serious romantic partnerships, toward which all of us should always be striving. According to the authors of a 2019 article in Archives of Sexual Behavior, focused on the US context, a “halo surrounds monogamous relationships . . . monogamous people are perceived to have various positive qualities based solely on the fact they are monogamous.” Other relationship models, or even just being persistently single, have often been seen as suspect, if not morally wrong.
Things are starting to change, though. Progressives, at least, increasingly exhibit a greater open-mindedness about intimate pairings that are not expected to be exclusive. There is growing awareness of alternatives to monogamy, such as polyamory: roughly, valuing or engaging in more than one sexual or romantic relationship at a time.