A friend of mine (a philosophy professor) and I were discussing issues of immortality, meaning, and love on Facebook. I explained to him that the love I feel for others in some sense 'seeks' immortality, as the depth of the feeling is such that without that belief, love would be almost too painful for me to bear. He expressed a diametrically opposed view, wherein love REQUIRES that we acknowledge the mortality of both the other and ourselves. This is, he said, because time is only a limited commodity and the time we spend with someone else is only valuable because there is a limited amount of it, and so spending time with someone is only really an act of love for the one for whom time is extremely limited.
Your friend seems to be maintaining that only a mortalist (one who maintains that bodily death spells the end of a person) can truly be said to love another person. Your friend's argument seems to be this:
1. The time spent with the beloved is valuable only because it is limited; therefore,
2. One cannot love without acknowledging the mortality of both lover and beloved.
First of all, I would say that this is a non sequitur. For even if we suppose that (1) is true, (2) is obviously false. Gabriel Marcel did not acknowledge the mortality of himself or his wife, and yet he loved his wife. (On this topic, Marcel is one of the people to read.) Whether or not love is genuine cannot hinge on whether one is right or wrong about the mortalism/immortalism question. It would be both churlish and absurd to say to Geach and Anscombe, "You two don't really love each other because you are immortalists!"
Your friend might respond by saying that the intensity of a love believed to be undying must be less than the intensity of a love believed to be as mortal as the lovers. To this I have two responses. First, the question of intensity is not the same as the question of whether the love is genuine. The genuineness of love varies independently of its intensity. Second, it is not obvious that a love believed to end with the lovers must be less intense. One could easily argue the opposite: if I believe that my love cannot survive bodily death, then I am more likely to practice something like Buddhist nonattachment with respect to the beloved and with respect to my loving of the beloved in accordance with the 'truth' that all is impermanent and therefore nothing is worthy of a full measure of commitment. In other words, you could argue against your friend that it is precisely because love can conquer death that you value it as highly as you do, and that because he does not believe this, he ought to value it less. You could say to him, "Look, if you believe that you and your love will soon pass away, then it is irrational of you to ascribe much value to yourself or your love. Impermanence does not intensify value; it argues lack of value!"
Saying this to your friend, you will not convince him ( I am quite sure of that!) but you will neutralize his argument and show that it is not compelling. And that is about all one can accomplish in a philosophical discussion. But it is also all you need to accomplish to be able to show that your intuitions are rationally acceptable.
As for (1), it is arguably false, and for some of the same reasons I have just given. If contact with the beloved ends utterly with death, then this could be taken to show that the contact was not so valuable in the first place on the Platonic-Augustinian ground that impermanence argues (relative) unreality and unimportance. I grant that this is not absolutely compelling, but it is as compelling as the opposite, namely, that impermanence increases value and importance.
I'm with you: love is a harbinger of Transcendence; it intimates of Elsewhere. You won't be able to convince your friend of this, but don't let that bother you. Any argument he can throw up, I can neutralize.
If you haven't read Augustine, you should. I also recommend P. T. Geach, Truth. Love, and Immortality: An Introduction to McTaggart's Philosophy (University of California, 1979), esp. the last chapter.