Group size two - and the nature of love

I need a whole post here about the powerful forces that draw people into groups of size two, what we call "relationships" with others, and that hold them there.

On one level, these forces are emotional, due to hormones, or otherwise built in. On another, these are a prototype of dyadic bonding that we need to have correct in our model of how people tend to form into clusters, groups, and larger operating structures and what keeps them there, and how such group membership alters their behavior, their psychology, their physiology, and their health.

One research finding for sure is that, in the USA, married males live longer than unmarried males, FWIW.