(Directory on Fear: https://www.philosocom.com/post/on-fear-and-the-right-to-resist-it )
The fear of finding oneself extensively (if not eternally) alone is a result of fearing to miss experiences, you wish, or have been taught to wish, you should, if not "need", to experience in order to have a life whose time has been well spent.
Therefore, those who are fearful to find themselves "forever alone", are afraid to miss social, romantic, and/or sexual experiences whose window of opportunity, is slowly being closed by the inevitability of time, until it is completely closed to you, never to be opened again.
Those who fear opportunities from the External World, are likely to lack them in the Internal World, a.k.a. in the wealth of their own solitude. What other reason would people be fearful of finding themselves "forever alone"? If you didn’t lack vividness, richness, and depth within your own solitude, why would you fear finding yourself having these well-preserved benefits, that you want to find in the External World? Why would you want to find and achieve what you have already found, achieved, and obtained?
If you want to be fulfilled by the possibility that you will be always single (even though even lifelong-single elders can find themselves in new relationships), you have to achieve the desired values, that you were taught that are present within the External World - through the walls of the Internal World.
AKA: to create and nurture these desired values, independently of romance.
People can be self-sufficient in many aspects, but we were taught we were not able to. People have potential, which they were taught they lacked. Some of our organs are capable of being stretched out over very long distances; some of us didn’t know they could. Now apply this to the metaphorical sense.
Sit and contemplate. Think of what you’re truly able to do, and what you're truly not able to do. Surprisingly enough, you will perhaps find out that you can do more than you initially thought you could by yourself. Realize your true limitations, and you will find out these barriers are farther away than you initially believed or were taught to believe.
For example, and this I have learned from my own experience, people are capable of spending days with almost no communication whatsoever, as long as they have things, or even just one thing, to occupy themselves with. It is just that we are socialized to create various dependencies without distinguishing them with our interpretations of necessity.
In reality, however, many of the things we associate with necessity are far from necessary, regardless of how many people think they are. Conformity does not lead to correctness, even though conformity may give us the impression of confidence and assurance.
The same logic can apply to romance and even to sexuality. Why do some of us desire more than others to have these in our lives? Some of us have a less vivid and rich internal life than others, and therefore we seek externally what we don’t have internally.
That is because if they had what they seek and were developed and strong enough internally, they wouldn’t seek it externally.
This is an insight schools and universities may not teach you because much, if not all, of the formal educational institutions take for granted the generalizing belief that every human is inheritably and inevitably a social being and is not capable of being largely solitary, let alone completely devoid of socially-oriented desires and needs.
And as I wrote previously, however - some of what we were taught is based on teachings that make us unaware of the lengths to which our potentials are capable of reaching.
To those who believe they may be "forever alone," I am definitely not saying or implying that you will indeed be single forever. You can be single forever, but that is your own choice, to either be determined to do so or to not learn of the things you do in the dating world that you shouldn’t do in order to have a successful "game" with your potential partners.