Falling in love comes at the cost of losing close friends, because romantic partners absorb time that would otherwise be invested in platonic relationships, researchers say.
A new partner pushes out two close friends on average, leaving lovers with a smaller inner circle of people they can turn to in times of crisis, a study found.
The research, led by Robin Dunbar, head of the Institute of Cognitive and Evolutionary Anthropology at Oxford University, showed that men and women were equally likely to lose their closest friends when they started a new relationship.
Previous research by Dunbar's group has shown that people typically have five very close relationships – that is, people whom they would turn to if they were in emotional or financial trouble.
"If you go into a romantic relationship, it costs you two friends. Those who have romantic relationships, instead of having the typical five 'core set' of relationships only have four. And of those, one is the new person who's come into their life," said Dunbar.
The study was designed to find out how people trade off spending time with one person over another and suggests that links with family and closest friends suffer when people start a romantic relationship.
Dunbar's team used an internet-based questionnaire to quiz 428 women and 112 men about their relationships. In total, 363 of the participants had romantic partners. The findings suggest that a new love interest has to compensate for the loss of two close friends.
Speaking at the British Science Festival in Birmingham, Professor Dunbar said: "This was a surprise for us. We hadn't expected it.
"When one does not see people, their emotional engagement with each other drops off and it does so quickly. What I suspect is that one’s attention is so wholly focused on the romantic partner that one doesn't get to see the other folks they had a lot to do with before, and so some of those relationships start to deteriorate."