From The Love Problem of the Student:
Love requires depth and loyalty of feeling; without them it is not love but mere caprice. […] Every true and deep love is a sacrifice. The lover sacrifices all possibilities, or rather, the illusion that such possibilities exist. If this sacrifice is not made, his illusions prevent the growth of any deep and responsible feeling, so that the very possibility of experiencing real love is denied. Love has more than one thing in common with religious faith. It demands unconditional trust and expects absolute surrender. Just as nobody but the believer who surrenders himself wholly to God can partake of divine grace, so love reveals its highest mysteries and its wonder only to those who are capable of unqualified devotion and loyalty of feeling. And because this is so difficult, few mortals can boast of such an achievement. But, precisely because the truest and most devoted love is also the most beautiful, let no man seek to make it easy. He is a sorry knight who shrinks from the difficulty of loving his lady. Love is like God: both give themselves only to their bravest knights.
Love is not cheap – let us therefore beware of cheapening it! All our bad qualities, our egotism, our cowardice, our worldly wisdom, our cupidity – all these would persuade us not to take love seriously. But love will reward us only when we do. I must even regard it as a misfortune that nowadays the sexual question is spoken of as something distinct from love. The two questions should not be separated, for when there is a sexual problem it can be solved only by love. Any other solution would be a harmful substitute. Sexuality dished out as sexuality is brutish; but sexuality as an expression of love is hallowed. Therefore, never ask what a man does, but how he does it. If he does it from love or in the spirit of love, then he serves a god; and whatever he may do is not ours to judge, for it is ennobled.
– C. G. Jung (1928)