What happens when someone flirts with your partner? New study might surprise you

Who does not want to be in a relationship with an attractive partner? But, if others find them equally appealing, it can lead to negative feelings, according to a recent study. A team of researchers led by Gurit Birnbaum found that people reacted to unsolicited attention given to their partner by feeling less desire for their partner, showing reduced interest in investing in the relationship, and becoming more interested in thwarting potential rivals. Also read | Relationship warning signs: From love bombing to gaslighting, 9 red flags you should never ignore
The researchers wanted to understand how unsolicited attention from others towards a current partner affects desire and relationship maintenance efforts. Does it make people desire their partner more, or does it perhaps make them wary of potential threats to the relationship, leading them to react defensively?
The researchers conducted three experiments to explore what happens in people’s minds and hearts when others show interest in their current partner. In each, participants were placed in situations where another person flirted with their romantic partner. 
In all studies, participants in committed relationships were exposed to situations where their partner either received unsolicited flirtatious advances (external attention condition) or had a neutral interaction with another person (control condition).
The study found that the meaning you attach to others’ attention changes once you’re committed to someone – when you’re single, external interest in a potential partner can serve as a valuable cue to their desirability; but in a committed relationship, that same attention may be perceived as a threat.
While some people might try to induce jealousy in their partner by seeking attention from others to feel more desired or secure, the aforementioned research shows this tactic can backfire. Instead of strengthening the relationship, it can damage the very connection it wants to enhance.
The results show that the fear of losing a partner can trigger a cascade of defensive reactions. To shield themselves from potential pain, people might create emotional distance and withdraw investment in the relationship, hoping to soften the blow if their fears materialise. 
At the same time, the anger ignited by others’ interest in their partner can manifest as confrontation towards these perceived rivals. These reactions, however, may be rooted more in retaliation than in genuine efforts to maintain the relationship.