Christian Jarrett surveys research into heterosexual relationships in which one partner was “poached” from a previous lover. He notes two studies that found that poached partners “reported progressively lower levels of commitment and satisfaction in their relationships”:
It makes intuitive sense that people who were poached by their partners showed less commitment and satisfaction in their existing relationship. After all, if they were willing to abandon a partner in the past, why should they not be willing or even keen to do so again? This logic was borne out by a final study of 219 more heterosexual participants who answered questions not just about the way their current relationship had been formed, but also about their personalities and attitudes.
[Researcher Joshua] Foster and his team summarised the findings: “individuals who were successfully mate poached by their current partners tend[ed] to be socially passive, not particularly nice to others, careless and irresponsible, and narcissistic. They also tend[ed] to desire and engage in sexual behaviour outside of the confines of committed relationships.” The last factor in particular (measured formally with the “Socio-sexual Orientation Inventory-revised”) appeared to explain a large part of the link between having been poached by one’s partner and having weak commitment to the new relationship.
The Dish 