Very interesting, so the exciting phase of "love" is basically designed by nature for maximization of the likelihood of creating babies. Then longer term hormones are designed to establish a stable and secure environment for those babies to be nurtured safely until they are ready to leave the nest so to speak, which in human terms is about fourteen to twenty years. I wonder what happens after twenty years to those hormones? Biologically there is probably no reason for them to exist beyond that unless you keep having more babies...
Perhaps they get extended to protect the family, so that the family can continue.
The bigger question is, what happens if the majority of society stop producing the long term ones?