I think most people have literally millions of potential, vaguely compatible mates with whom they could live more or less satisfied lives, provided only that they are willing to compromise of some aspects of their life, out of a greater desire to settle down with one person (and potentially raise a family). I don't think there are any exceptions to that. Who they actually pick ends up being more about the perceived degree of closeness of the potential match versus the degree of compromise required versus their perceived desire to be in a(ny) relationship. Consider it a three-way, dynamic & interdependent, balancing act. If there's an equilibrium, it's considered love. Sometimes it's a stable equilibrium, sometimes an unstable one (in which case separation, and "falling out of love" occurs). Obviously, I appreciate that people don't perceive it that way, but those are nonetheless the factors at play.
The idea of a single soulmate is, I think, faintly ridiculous at best, though I can certainly grasp why it's a pervasive & emotionally appealing construct. I also think that most people intensely overvalue the concept of romantic love, to the detriment of their overall potential maximum net happiness over the course of their lives. That's not a criticism; people are free to choose to prioritise whatever they want and good luck to them. I hope they will be happy, and rejoice if they are. I just happen to think they're somewhat unwise.
A lot of the practical history of the family and its structures is down to economic/resource pressures that we - as an increasingly wealthy & complex society - are slowly finding ways of working around (note the vast expansions of healthcare, social care, welfare safety nets, transportation networks, employment options, luxury consumption, etc, etc, etc). I think that's a fairly irreversible process. What remains to bind couples together on a vaguely permanent basis is increasingly only the residual ideal of love. It will be interesting to see whether that remains enough as the generations continue to pass. It will for a long time I think, at least in theory (in practice, people will marry increasingly late, and even so, divorce rates will remain high), but at some point, a new concept that fills the same human need to have a manifest destiny, will probably overtake it in the popular imagination.
Interesting question, for sure.