Figuring out who to marry is a big decision. You have to think about what your marriage will look like five, 10, 20 and 50 years from now, and that's a hard thing to know. You never know what trials will hit your marriage, and if you'll be able to get through everything life throws at you.

You want to make sure you're marrying the right person, but how do you know who that person is? How do you know if you're making the right decision? A study from the National Bureau of Economic Research has the answer, and it's simpler (and more surprising) than what you might think.

According to Huffington Post, the study explored what made marriages happy. They found that, "The big takeaway from their research was that those who considered their spouse a 'best friend' boasted the highest levels of happiness."

There you have it — if you marry your best friend, you'll have an overall happier marriage. The study also found "The well-being benefits were twice as large for those couples."

So if you're deciding whether you should marry someone, think about your relationship as friends. When you marry your best friend, you're so much happier and more satisfied in your marriage. Here are 8 signs you and your sweetheart are best friends:

1. You trust each other

You know your sweetheart would never do anything to hurt you, and you would never do anything to hurt them. You completely trust and respect each other.

2. You love being together

You never get sick of each other, and you want to spend whatever time you have with each other. But you're also not afraid to spend time apart, because you know you'll always come home to each other.

3. You make each other better

You're constantly trying to better yourselves, because you want to be the best you for each other.

4. You put each other first

You prioritize each other above everything else.

5. You talk about everything

You don't have secrets, and you love talking about your days together because you're truly interested.

6. You don't want them to change

You just love everything about them — even their little, weird quirks.

7. You really like them

You don't just love them — you would like them even if you weren't in love.

8. You couldn't live without each other

You can't picture a life without your sweetheart right by your side.

Building a friendship with your spouse is so important. Whether you're thinking about getting married, you're newlyweds or you've been married for 30 years, it's never too late to become best friends with your sweetheart.