Psychoanalyst Adam Phillips addresses this central paradox with uncommon clarity and elegance in Missing Out: In Praise of the Unlived Life (public library).
Phillips writes:
All love stories are frustration stories… To fall in love is to be reminded of a frustration that you didn’t know you had (of one’s formative frustrations, and of one’s attempted self-cures for them); you wanted someone, you felt deprived of something, and then it seems to be there. And what is renewed in that experience is an intensity of frustration, and an intensity of satisfaction. It is as if, oddly, you were waiting for someone but you didn’t know who they were until they arrived. Whether or not you were aware that there was something missing in your life, you will be when you meet the person you want. What psychoanalysis will add to this love story is that the person you fall in love with really is the man or woman of your dreams; that you have dreamed them up before you met them; not out of nothing — nothing comes of nothing — but out of prior experience, both real and wished for. You recognize them with such certainty because you already, in a certain sense, know them; and because you have quite literally been expecting them, you feel as though you have known them for ever, and yet, at the same time, they are quite foreign to you. They are familiar foreign bodies.
This duality of the familiar and the foreign is mirrored in the osmotic relationship between presence and absence, with which every infatuated lover is intimately acquainted — that parallel intensity of longing for our lover’s presence and anguishing in her absence. Phillips writes:
However much you have been wanting and hoping and dreaming of meeting the person of your dreams, it is only when you meet them that you will start missing them. It seems that the presence of an object is required to make its absence felt (or to make the absence of something felt). A kind of longing may have preceded their arrival, but you have to meet in order to feel the full force of your frustration in their absence.
[…]
Falling in love, finding your passion, are attempts to locate, to picture, to represent what you unconsciously feel frustrated about, and by.
Missing Out, previously discussed here, is a magnificent read in its totality. Complement this particular portion with Stendhal on the seven stages of romance, Susan Sontag on the messiness of love, and the great Zen teacher Thich Nhat Hahn on how to love, then revisit Phillips on balance, the essential capacity for “fertile solitude,” and how kindness became our guilty pleasure.