A strong friendship is the secret to a long-lasting romantic relationship, new research suggests.
Researchers found that valuing your friendship with your partner helps create relationships with more commitment, more love and greater sexual satisfaction.
People who put more emphasis on trying to satisfy their personal needs or desires through their relationship are less likely to sustain the bond in the longer term.
'Romantic relationships are, at their core, friendships,' said the study's lead author Laura VanderDrift, of Purdue University in Indiana.
'As such, it may be the case that valuing that aspect of the relationship fortifies the romantic relationship ... and serves as a buffer against breaking up.
'The results indicate that valuing the friendship aspect of a romantic relationship is important to relationship quality.
'It seems likely that placing greater importance on the friendship component of the relationship relative to other components (e.g. sex) may promote lasting relationships.'
The psychologists wrote that relationship failures can lead to negative emotions, feelings of insecurity and reduced physical health.
But they added that friendship is a 'defining characteristic of love' and suggested that understanding the causes of break ups could help couples avoid that fate.
The team, who report their findings in the Journal of Social and Personal Relationships, conducted two experiments.
The first involved 190 students who had been in a relationship for an average of 18 months at the start of the study.
They filled out questionnaires designed to assess the amount of investment they put into their relationship generally, different aspects of their relationship and their future hopes.
Four months later they were contacted again, by which time a quarter (27 per cent) were no longer with the same partner, and asked further questions about their relationship.
People who had scored highly for investing in the friendship aspect of their relationship were also more likely to score highly on romantic commitment, love and sexual satisfaction. They also tended to see increases in these elements over the four months of the study.
Crucially, those who put the most effort into building a strong friendship with their partner were less likely to have broken up.
The second experiment involved 184 students, who had been in relationships for 16 months on average.
They were asked to rate the value they attach to aspects of a relationship such as companionship, security, sex, self-improvement and experiencing new things on a scale of one (not at all important) to nine (extremely important).
People who rated the need for companionship and affiliation highly also tended to score higher for romantic commitment and sexual fulfilment.
Those who rated personal needs as more important did not score as highly on commitment or sexual fulfilment.
The authors said that further research could look at the specific kinds of behaviour that influence the link between strong friendships and lasting relationships.