Rilke, "On Love - and other difficulties"

I am of the opinion that "marriage" (partnership, union, etc.) as such does not deserve as much emphasis as it has acquired through the conventional development of its nature. It does not occur to anyone to expect a single person to be "happy,"—but if he marries, people are much surprised if he isn't! [...] Union is, in many respects, a simplification of one's way of life, and the union naturally combines the forces and wills of two people so that, together, they seem to reach farther into the future than before.—Only, those are sensations by which one cannot live. Above all, a partnership is a new task and a new seriousness,—a new challenge to and questioning of the strength and generosity of each partner and a great new danger for both.

It is a question in union, to my feeling, not of creating a quick community of spirit by tearing down and destroying all boundaries, but rather a good partnership is that in which each appoints the other guardian of his solitude, and shows him this confidence, this trust, the greatest in his power to bestow. A togetherness between two people is an impossibility, and where it seems, nevertheless, to exist, it is a narrowing, a reciprocal agreement which robs either one party or both of his fullest freedom and development. All companionship can consist only in the strengthening of two neighboring solitudes, whereas everything that one is wont to call "giving oneself" is by nature harmful to companionship: for when a person abandons himself, he is no longer anything, and when two people both give themselves up in order to come close to each other, there is no longer any ground beneath them and their being together is a continual falling. So, there is scarcely anything more difficult than to love one another. That it is work, daily labor, God knows. For one human being to love another: that is perhaps the most difficult of all our tasks, the ultimate, the last test and proof, the work for which all other work is but preparation. But, once the realization is accepted that even between the closest human beings infinite distances continue to exist, a wonderful living side by side can grow up, if they succeed in loving the distance between them which makes it possible for each to see the other whole and against a wide sky!

Therefore this too must be the standard for rejection or choice: whether one is willing to stand guard over the solitude of a person and whether one is inclined to set this same person at the gate of one's own solitude, of which he learns only through that which steps, festively clothed, out of the great darkness.

[...]

Love consists in this, that two solitudes protect and touch and greet each other.

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I hold this to be the highest task of a bond between two people: that each should stand guard over the solitude of the other. For, if it lies in the nature of indifference and of the crowd to recognize no solitude, then love and friendship are there for the purpose of continually providing the opportunity for solitude. And only those are the true sharings which rhythmically interrupt periods of deep isolation...

—Rainer Maria Rilke, Letter to Emanuel von Bodman, Aug 17, 1901 (while Rilke was 26).