As human beings, we are designed for relationship. No one is meant to do life 'alone'. We are all better off when we are connected with other people. It's part of our inner need to belong. Of course, experiencing a sense of belonging takes effort and time (the very word "belong" comes from two words "be … long"). It also requires a degree a compatibility, common interest, shared values and trust. 
Our relationships can be seen as occurring in a series of concentric and widening circles.
1. The crowd. We all know and connect to hundreds and even thousands of people in our lifetime. This includes the many casual interactions we have – at home, at school, at work, out shopping and in various groups we may be a part of (sport, church, community organisations).
2. Acquaintances. These are the people we know by name and have some history with.
3. Casual Friends. These are people we hang out with from time to time. We know more about them, and have more shared experiences. 
4. Close Friends. These are the few people we spend the majority of our time with. We have common interests and a closer heart connection with them. There is also a mutual replenishment that comes from the interaction because both people are contributing, rather than one person always taking the lead to initiate things or ask all the questions. Your time with each other could be described as energising, rather than draining. 
Jesus himself loved the crowd, had many acquaintances, yet had 70 people who he spent more time with and out of which he had 12 close friends, three of whom were his best friends. Yes, relationships are ‘spatial’ or defined by different degrees of proximity. 
Being friendly and outgoing is an important part of living together as humans. Every person we meet is a potential friend (whether casual or close), and should be treated as such – with worth and value.
But do we really need MORE relationships? Like a LEGO block, we all have different capacities for connection. If you have no friends, you have ample space for more relationships and would benefit from making an effort to meet and get to know more people. In contrast, if your LEGO block is full, you don't really have the capacity to take on a heap of new relationships. 
Maybe it is time to evaluate and do a 'relational stocktake'. Otherwise, we end up continually 'skimming' with a large group of casual friends but never really going deep with any of them. We are always in a hurry and end up relating superficially. I know this feeling, especially having been part of a church with thousands of people for so many years. 
Many friendships can be work or career based (just like school friends). When we stop working together we discover there’s not much left to the relationship. Or maybe you recently moved house or started to attend a different church or social group. As a result, your friendships change.
I was born in Melbourne, Australia but moved to the USA when I was 10 years old. I lived there until I was 18 when our family returned to Australia. Moving at age 10 was an adventure while returning at 18 was much harder as I had an established network of friends. I kept in touch with some friends in the USA but gradually lost touch with most. They were part of my past but not part of my future. It was a time to start again and make new acquaintances, some of whom gradually became close friends. 
This is just part of how life works. You are no longer in the same environment or context and so it tends to be ‘out of sight out of mind’, unless there is intentional and mutual effort to continue the relationship and sow into new areas of commonality. Otherwise, everyone simply gets on with their own life.
Could life be better for you through spending more quality time with fewer people – your family and the friends that mean the most to you at this time in your life? 
[See also my BLOG posts about Connecting with People]