We're pretty sure you have your own measure of telling if you're in a healthy and happy relationship. You and your partner trust each other 100 percent; you guys know when to give each other space; you guys are still affectionate and in love after years and years of being together. But research also weighs in on what really makes a relationship healthy and what makes it last, and it's actually being friends with your partner.

A study in the Journal of Social and Personal Relationships found that couples who valued friendship with each other the most are more committed, more in love, and more sexually satisfied than couples who weren't friends with one another.

The study, done by researchers at Purdue University, had 190 students who've been in a relationship for one year and five months gauge how much they valued and invested in the relationship. The researchers followed up on the respondents' relationship status four months later. They found that some have already broken up with their partners. When they went back to their survey results, the researchers found that the couples who were still together scored high in the friendship aspect of their relationship. More importantly, they found that friendship even made the love/romance grow and furthered the sexual gratification, and that it was less likely to make the relationship end.

So if your partner was your friend first before your partner, is/has become your best friend, congrats. You got someone for the long haul.

This story originally appeared on Cosmo.ph.

* Minor edits have been made by the Femalenetwork.com editors.

PHOTO: Flickr Creative Commons/Howard Galicia