Write a letter, now, from the version of you who is inside this love to the version of you who will, one day, no longer be. Not because the love will end — though it might — but because all loves are eventually no longer ongoing in the present tense, even the ones that last fifty years. The future you, whether widowed or partnered-still or long-separated, will have a relationship to this present love that is different from the one you have now. And the present you has access to something the future you will not: the temperature of it, the texture of it, the specific weight of it in your chest as you stand in the kitchen waiting for the kettle.
The letter is for that future self. To remind them. To preserve, in language, what time will erode.
Future-you will forget things. This is not a moral failure; it is a feature of memory. The specifics will fade. The exact way they laughed at the inside joke. The smell of their hair after the rain. The particular argument that you both still bring up because it became, in retrospect, hilarious. The Sunday morning routine. The way they pronounced your name when calling from the next room. These will not be available to future-you in the way they are available to you now. Future-you will have a summary. The summary will be true but lossy. You can compress some of the loss by writing it down now, while you still have the high-resolution version.
This is, in part, a Law Five exercise — Revise — but turned in an unusual direction. Most revision work asks you to update your view of the past or your sense of the future. This exercise asks you to preserve the present for a future revision you cannot yet make. It is an act of anticipatory generosity toward a version of yourself who will be older, possibly sadder, possibly wiser, and definitely unable to fully retrieve what you currently take for granted.
Joan Didion, in The Year of Magical Thinking and especially in Blue Nights, returned compulsively to the question of what memory keeps and what it discards. The specific phrases. The specific gestures. She found, in her grief, that she had not preserved enough — that the texture of her husband and her daughter had begun to thin even within months, and that what remained was a sketch where she wanted a portrait. The letter to your future self is, among other things, a defense against this thinning.
Several things belong in such a letter:
The specifics that no third party would care about. The way they always say sorry in a particular tone when they bump into furniture. The thing they always order. The face they make when they are trying not to laugh. The unmemorable becomes the unrecoverable. Write it down.
The thing about them that you would mention first if you had to explain to a stranger why you chose this person. Not the resume version. The actual thing. Future-you will want to remember why, and the answer will not be in the photographs.
The argument that nearly broke you and did not. The shape of the repair. The specific sentence that one of you said that brought it back. You will need this story later, possibly to tell someone, possibly to remember in a moment when you are tempted to forget that repair is possible.
What you have learned from them. Not abstractly. Specifically. What habit did you develop because of them. What instinct did you sharpen. What part of you exists now that did not exist before them. These are the inheritances they have given you whether or not the relationship lasts. Write them down so you can carry them honestly later.
What you wish you had said more often while they were still in the present tense of your life. This is the hardest section, because to write it is to admit there are things you are still postponing. Write them down. Then say them, too. The letter is for future-you, but the act of drafting it changes present-you, which is part of the point.
What you would want this love to have stood for, when future-you looks back at it. The shape of meaning you would want the love to have carried. Not what you would tell others. What you would tell yourself, in a quiet room, about what this connection was for, in your one life.
The letter is not for them. It is not a Valentine. It is a private archive. You write it because future-you deserves to inherit, with as much fidelity as you can preserve, the specific texture of what you are currently inside.
And here is what nobody tells you: the act of writing the letter will change how you are inside the love right now. You cannot describe what you are paying attention to without paying attention. You cannot itemize what you would want future-you to remember without becoming, in the act of itemizing, more present. The letter is therefore a double gift. It preserves something for the future, and it sharpens something in the present. Future-you will receive an archive. Present-you will receive a focused attention they did not know they were neglecting.
Do not over-edit. Do not perform. Future-you does not need literature. Future-you needs evidence. Names, details, dates, smells, sentences they actually said. The more specific, the more valuable later. The general will fade with everything else. The specific will remain.
Write the letter. Seal it. Put it somewhere. You will read it again one day in a state of mind you cannot currently imagine. The you who reads it then will be grateful — sometimes piercingly so — that the you who wrote it took the time.