Saying “I love you” to someone still alive, other than a romantic partner, is difficult. Though I would gladly admit that I love my parents (and family), and would say so to anyone else who would bother asking, I would not say it directly to them.
However, if I do imagine any one of them on their deathbed, perhaps as an invalid, or if they were institutionalised due to a severe case of senility, I would be more willing to tell them that I loved them more directly.
The difficulty in proclaiming love, when knowing that one still has a long way to go with another, is in integrity.
By saying “I love you” to another, it gives the other a power over you.
Here is a little scenario for you: Imagine that due to other commitments you were not able to attend a family function.
“What do you mean you can’t come? You promised!” they would say. And even before you can get another word out, they continue, “don’t you love us? You told us so. And yet, here you are rejecting our request for a short get-together! What a cheat!”
Of course, it probably won’t be as dramatic as this. Most times, the other person would just be thinking it inside his or her own heart, “he says he loves me, but look what he has done. I wonder what other lies he tells us.”
But when a person you love is on his or her deathbed, and you know that the future you have with him or her is short, saying “I love you” gives little chance for it to be a lie. There is simply not enough time or opportunity for those words to become untruths.