I wouldn’t say its a moral absolute just because there is so much room for personal interpretation. Even when it comes to loving those closest to us, people disagree on the best way to do that.
Also, the commandment to love your enemies has to be balanced with the commandment to love your neighbour, etc. Our obligations towards those closest to us might conflict with the obligations we have to people we are less responsible for, e.g. our enemies in a war.
But one thing it means for sure is what we should remember that these people who are on the opposite side of a conflict are children of God like we are, and that God loves them and desires that they be saved. We are also forbidden to hate anyone, even our enemy. We might still go to war with them if necessary, but never out of anger or a desire for vengeance. We have to sincerely do our best to balance our duties towards ourselves, our families, our countrymen, and the duty to love the enemy.