Sue and Dan are in a relationship. Their friend, Matt, is romantically interested in Sue. If Matt tries to “steal” Sue away from Dan, then he is doing what researchers call “mate poaching.” To try to poach Sue, Matt might do things like insult Dan, try to compete with Dan, tell Sue that she could do better, and/or try to keep Sue from hanging out with Dan. There is no shortage of examples on TV shows and movies of one person poaching their friend from an existing romantic relationship (e.g., Made of Honor). But outside of Hollywood, is mate poaching by friends common?
In a recent study, researchers followed cross-sex friends for a few weeks.1 The researchers found that the more romantically interested people were in their attached friend, the more they engaged in poaching behaviors, which included the ones described in the previous paragraph (e.g., insulting the friend’s romantic partner). The results also indicated that men made more frequent poaching attempts towards their friend than women did. How effective were these poaching attempts?
Let’s imagine that Matt and Sue were participants in the above study. The more Matt engaged in poaching behaviors (e.g., the more he insulted Dan and tried to keep Sue away from Dan), the less committed Sue was to her relationship with Dan one week later. She later also saw Matt as more desirable as a romantic partner, and she was more interested in being romantically involved with Matt. Thus, making multiple poaching attempts was effective at making romantic relationships less stable over time.
In light of these findings, it makes sense why some folks are worried about how close their romantic partner is to cross-sex friends (read here about feelings of jealousy that frequently occur in this situation). However, most friendships in this study were innocent. On average, people rarely tried poaching their friend. Additionally, on average, the attached friend had very little-to-zero romantic interest in their cross-sex friend and was very committed to their relationship with their romantic partner. It was also rare for people to actually leave their romantic partners for their friend in this study. So, apparently, there is nothing to worry about for most cross-sex friendships!2
TL;DR: Attempts to poach a friend from an existing romantic relationship can be effective over time, but most friends are just friends.
1Lemay, Jr. E., & Wolf, N. R. (2016). Human mate poaching tactics are effective: Evidence from a dyadic prospective study on opposite-sex “friendships.” Social Psychological & Personality Science. Online First. doi: 10.1177/1948550615623843
2Read more about cross-sex friendships here
Dr. Lisa Hoplock – Science of Relationships articles | Website/CV
Lisa’s research examines how personality traits like self-esteem and attachment influence interpersonal processes in ambiguous social situations — situations affording both rewards and costs — such as social support contexts, relationship initiation, and marriage proposals. 
