It's also important to keep in mind that within that time span the woman would most likely be pregnant

Also you have the pressures of a hunter gathering environment or an environment that is pre-industrial

Which helps to maintain the relationship out of necessity and the need for the children to survive

It also means people need to be social and maintain bonds of fellowship and family in order to survive

Human beings respond to incentives and without those incentives the fabric of our society starts to fray

Human beings are lazy and it's a reason why our social bonds are so decayed the because we don't really need them

If you live in a modern and advance society in the West

Great point you have made their just a lot that goes into that

Have you thought about writing your own stuff?