Having a strong friendship bond with your partner is the secret to having a long-lasting romantic relationship, scientists claim.

Researchers found that lovers who are also close friends enjoy better sex, more love and greater commitment. However, researcher found that people who are more interested in satisfying their personal needs and desires through their relationship are less likely to stay in a long-term relationship.

"Romantic relationships are, at their core, friendships," researchers wrote in the study published in the Journal of Social and Personal Relationships.

"As such, it may be the case that valuing that aspect of the relationship fortifies the romantic relationship against negative outcomes and serves as a buffer against dissolution," they added.

To look at how friendship affects romantic relationships, researchers conducted to experiments. 

For the first experiment, researchers recruited 190 students who had been in a relationship for an average of 18 months at the start of the study.  Participants were asked to fill out surveys designed to measure the amount of investment they put into their relationship, different aspects of the relationship and what they hope for in the future.  Researchers then contacted the participants four months after the start of the study to ask follow-up questions about their relationships. 

The results revealed that 27 percent were no longer with the same partner.  The findings show that those that those who had high scores for investing in the friendship aspect of the relationship were also more likely to score highly on romantic commitment, love and sexual satisfaction.  Researchers said that those who had the strongest friendship bonds with their partner also tended to see increases in romantic commitment, love and sexual satisfaction over the four months of the study period. Most importantly, researchers said that lovers who put most effort into building a strong friendship with their partner were also less likely to have broken up.

In the second experiment, researchers recruited 184 students who had been in relationships for 16 months on average.  Participants were asked to rate how much they value relationship aspects such as companionship, security, sex, self-improvement and experiencing new things on a scale of one to nine.

Researchers found that those who rated the need for companionship and affiliation as high on the scale also tended to score higher for romantic commitment and sexual fulfillment, whereas those who rated personal needs as more important did not score as high on commitment or sexual fulfillment.

In the future, researchers hope to identify specific kinds of behavior that influence the how strong friendships connect with lasting romantic relationships.