It's a non-quantifiable scenario, whether kids or wife come first. Who do you love more? Does your wife get more Christmas presents more of your time? Does she get more of your time?
In a divorce, both relationships have failed. The base purpose of marriage is to procreate, not that it is necessary, but on some level we realize that this is truth in Western Civilization.
As you say, love is not quantifiable, and it's not a question of who you love more, but to put a different angle on this... in some senses putting your marriage first is putting your kids first.
Kids want a stable, loving environment, and will learn about adult relationships by observing how their parents treat each other (as well as how they treat them). Being around a strong marriage is pretty much the best gift (as well as time) that you can give kids.
I always thought it was a mistake for my parents not to spend more time together outside of their parental roles, and even when I was a kid I could see these as seeds of later turmoil. So whilst this advice isn't directly for you, I'd advise any parents to make some time to enjoy together, away from their kids (so long as the kids are old enough to be looked after by others). Its not selfish if everyone wins.
If you want to argue base purpose, the base evolutionary purpose of pair bonding (which leads to marriage) is to ensure good child care for ones kids. Evolutionarily, men who participate in serial marriage, having kids with each, are very successful. Even though their relationships are not.
Evolution does not care whether your children are happy and healthy. It cares that you have a bunch of them, and they have children in turn.
I am not very successful evolutionarily. Nor do I strive to be.
In a divorce, both relationships have failed. The base purpose of marriage is to procreate, not that it is necessary, but on some level we realize that this is truth in Western Civilization.