Working on an article on conjugal love for the NCR, I've been combing through my "love quote" files, and just came upon this absolute gem from Benedict XVI in Deus Caritas Est: [my emphasis]
Even if eros is at first mainly covetous and ascending, a fascination for the great promise of happiness, in drawing near to the other, it is less and less concerned with itself, increasingly seeks the happiness of the other, is concerned more and more with the beloved, bestows itself and wants to “be there for” the other. The element of agape thus enters into this love, for otherwise eros is impoverished and even loses its own nature. On the other hand, man cannot live by oblative, descending love alone. He cannot always give, he must also receive. Anyone who wishes to give love must also receive love as a gift. Certainly, as the Lord tells us, one can become a source from which rivers of living water flow (cf. Jn 7:37-38). Yet to become such a source, one must constantly drink anew from the original source, which is Jesus Christ, from whose pierced heart flows the love of God (cf. Jn 19:34).”
In one way, as our love grows, we become less concerned with ourselves, more concerned with the other. Instead of just wanting to possess him for the sake of our own happiness, we want to "be there" for him—help become himself, bear his burdens, fulfill his vocation. And on the other hand, we grasp the mysterious fact that in order for us to be ourselves and live our own vocation, we need his help, his love, the gift of him.
This is "the great mystery" at the heart of everything human.