Not the feeling of affection. That's a natural emotion. No one had to teach you that, and it's not love-- agape love. I mean, who taught you how to give selflessly to another person, not counting the cost, day in and day out, without complaint? Loving selflessly does not come naturally to us-- been around a three year old lately? So, who taught you?
Your mother? Father? A grandparent? Your spouse? A close friend?
In the Vatican II document Gaudium et Spes, the Church teaches that "Parents . . . are, so to speak, the interpreters of . . . [God's] love." When I stop and think about this, I can't help but get a little bit nervous. After all, "selfless" isn't always the best word to describe me, and yet there it is in the Catechism of the Catholic Church, 2214: "The divine fatherhood is the source of human fatherhood." One way to translate this is that I am to reflect God for my children (and my students). I am to "interpret" God's Son-sacrificing, pain-enduring, grave-shattering, unending love in a way that they can come to know God more closely, and (as if that weren't hard enough) desire to love in that same way someday themselves. Thankfully I (and you, too) am not on my own in this. Supporting me in this endeavor are my Savior, my Heavenly Father, the Holy Spirit, the entire communion of saints, and a worldwide (and local) Church. (I'm going to need all the help I can get.)
Like I said, I'm not the poster child for selflessness. Are you? Sure, we all have our moments, right? But, a good examination of conscience for both parents and teachers might be to look at our own actions through the eyes of our children/students: Do I work without complaint? Do I set aside my own wants in the service of others? Do I show my children/students "a still more excellent way" (1 Cor. 12:31)-- the way of love?
The divine fatherhood is the source of human fatherhood. (Catechism of the Catholic Church, 2214)
Parents . . . should realize that they are thereby cooperators with the love of God the Creator, and are, so to speak, the interpreters of that love. (Gaudium et Spes #50)