A general rule found in research, known as "no cycles of four" within two romantic heterosexual couples, is that people rarely date the ex-partner of their own ex-partner's new boy - or girlfriend. what explanation is given for this finding?

Sociologists Bearman, Moody and Stovel have found that individuals rarely date the ex-partner of their own ex-partner's boyfriend or girlfriend. Their findings were very significant in the study of how sexually-transmitted diseases spread, as this lack of "cycles of four" means that diseases do not propagate in small, closed cores, but in spanning trees.

However, the reasons for this pattern are not well understood. One of the possibilities is that people try to avoid "jealousy." There is also the possibility that humans naturally avoid "too much closeness," which could explain why, despite the situation not being a written rule, it is almost nonexistent in the populations they studied.

Nevertheless, the most likely explanation given in the article is that this type of pattern represents a loss of status, and it is thought of as a "seconds partnership." So the avoidance could have more to do with not losing face than with an actual aversion towards the fourth person.