As you can see from the headline, the science shows that humans can only maintain a limited number of relationships. Below is the key conclusion of the article, based on British psychologist Robin Dunbar's research. This has since become known as "Dunbar's Number."
"The innermost circle is just five people—friends or family members—that you feel emotionally closest to. These are the shoulders you cry on, the people you contact at least once a week. Then comes a layer with 10 additional good friends you see at least once a month. About 60% of your social attention goes to these 15 people, Dunbar said.
Farther out is what he calls your 'weekend backyard barbecue party group' a total of 50 people, including the 15 that you see regularly.
Finally, Dunbar describes an outer ring bringing the total to 150 and including an additional 100 people you would invite to your once-in-a-lifetime big events like a wedding or “wouldn’t feel embarrassed about going up to them and slapping them on the back if you bumped into them at 3 a.m. in the departure lounge at Hong Kong Airport.”