New here, so don't know my way around the software yet. I don't think that it is a question of love or about love being less or more etc. Love is infinite. As the population grows, have you noticed children born without the capability of love?
That being said, as you add more partners, have bigger families, etc. Sometimes, not always, but sometimes the stress also goes up. It may not be a question of love becoming less, but stress becoming more.