I don't disagree with that pattern, but I think I see it in a little different of a framework. I am no advocate of everyone being in relationships, much less long-term committed ones, but these are my thoughts on the how and why of them, when and if they do occur. I see them, at their best, as mutual outpourings of altruistic love and a mutual exercise of free will, a sacrifice and a risk undertaken in hope of mutual gain.
Much like the above pattern demonstrates, each person in a relationship has different needs, tendencies, and internal clocks they're running on, so at times the two come together in the right way, and at other times the two draw apart and create tension. Both people's individual lives undulate to some degree on their own patterns, though the longer they're together the more their patterns impact one another. This means that sometimes one partner seeks the other more, and other times there is mutual drawing together or pushing away. But part of the draw of the other is that they
are foreign and separate in many ways. It makes them interesting and it brings a whole new set of strengths into your life.
A long-term committed relationship is making the choice that the good times and mutual support are worth the tension and stress of the harder times. And of course that is not for everyone, and it takes a particularly mutually-beneficial relationship for the symbiosis to become worth more than the individual freedom. The bright side is that even if you draw apart at some point, inevitably you fluctuate back together again, as your lives are intertwined. So of course there may be some moments during the relationship at which it is more stressful than beneficial, but the long-term gain is worth the short-term sacrifice. And over time you begin to learn one another's patterns, too, so it becomes increasingly easier to predict and relate and influence one another. You increasingly act as a symbiotic whole, maximizing mutual benefit and minimizing individual loss.
But eclipsing that - in terms of there being a "better person" out there - I used to feel that strongly, and it ate away at me. The truth in my case was that it was an escape for when I didn't want to look at myself and my selfishness critically. Eventually I got to the point in my relationship where I realized how much I was obsessed about my own happiness, and a relationship can't work like that. There was this article that circulated Facebook not long ago entitled
Marriage Isn't for You that addressed it in the way that I tend to see it now. Much of the beauty and strength of a long-term committed relationship is that you willingly close your eyes to other options because you care about the other so much. Other options just cease to matter when you prioritize making your partner happy and fulfilled. I think it is akin to the shift parents experience when they have their children, in that suddenly perspective shifts away from "I". Once the frame of reference changes, the reward system changes too. Getting everything you want is no longer the ultimate pleasure; watching your partner flourish is.
But, unlike with parenting, this perspective shift has to be mutual to last, as the relationship is a willing choice. You are absolutely right about the fear of being alone; the truth is that either person could end it with nothing more than a whisper. In terms of marriage or equivalent lifelong commitment, you willingly sacrifice your future freedom and take the risk that you may be investing potential in something out of your hands. It's a biting truth, that in a way we are no less alone when married than we are when we are single. We are just more vulnerable. That marriage is some sort of failsafe protection from loneliness is an illusion, though certainly many fall prey to it. Worse is the illusion that having someone's child will "lock" a marriage. Commitment is a leap of faith, essentially... ultimately all of our choices are. You bind yourself to the other in the hope that they too will bind themself to you, and together you can begin to fulfill each others' longings and provide each other with support and warmth through the good and the bad of life. It's idealistic, to be sure, but you can't reap the ultimate gain unless you are willing to put yourself and your future on the line. The key is that the more it is done out of altruistic love, the less of a risk it is.