Why do we have an urge, a social prerequisite, to find someone? To find another human being to attach oneself to?

I understand the biological impulse to reproduce, and therefore engage in sexual intercourse, but why must this biologically-driven urge be coupled with human emotion?

Why can we not be happy by ourselves?

Why is it expected of us by the majority of humanity, ourselves included, to “find” someone? To enter into not just physical, but chemically-driven emotional relations with this illusive “someone”?

Does our biological impulse to reproduce, and/or engage in sexual intercourse, deprive us of the possibility of being happy on our own?