Others who could replace you in your relationship typically provoke jealousy. However, your partners’ same-sex friends can also illicit jealousy. Across two studies with over 200 participants, researchers found that partner-friend jealousy was greater for those who: (a) considered their romantic relationships more important to their lives, (b) were less close to their own friends, and (c) perceived their partner was less committed to the relationship. Perhaps for their own benefit, those experiencing greater partner-friend jealousy were more likely to put down or derogate their partner’s friends in an attempt to undermine the partner’s bonds with others.
Gomillion, S., Gabriel, S., & Murray, S. L. (2014). A friend of yours is no friend of mine: Jealousy toward a romantic partner's friends. Social Psychological and Personality Science (Online) doi: 10.1177/1948550614524447