The first thing that gets dropped
On holding ordinary commitments while caring, and treating them as fixed rather than negotiable.
The things that go first are never the important ones. They are the ones nobody else notices you have stopped doing: the Tuesday evening thing, the walk, the friend you used to telephone without a reason. They go because they are the only items in the week that produce no consequence when missed, and because missing one, on any particular week, is obviously the right decision.
It is obviously the right decision every week. That is the whole mechanism. Nothing was ever given up. Each individual instance was simply postponed, and after a year the thing has stopped without a decision ever having been made about it.
Fixed, not negotiable
The only defence that works is to move one or two of these commitments out of the category of things that can be rearranged. Not all of them. One or two, chosen deliberately, and then treated with the same rigidity as a commitment made to somebody else.
This sounds harsh and it is really a form of honesty. A commitment that is always available to be moved will always be moved, because there will always be something with a stronger claim on the evening. Declaring in advance that a particular evening is not available is not selfishness. It is the recognition that the alternative is not fewer commitments but none.
Choose things with other people in them
When choosing what to protect, prefer the commitments that involve other people expecting you. A solitary intention to read more is admirable and it will not survive, because nothing external reinforces it. A weekly arrangement where somebody notices your absence has a structure holding it up that does not depend on how the week has gone.
This is also the practical answer to the narrowing that carers describe, where the circle of people they see contracts to those involved in the caring itself. A commitment that puts you in a room with people who are not discussing the arrangement is doing two useful things at once.
Say what it is, plainly
Tell the relatives involved which evening is fixed, and say it as a fact rather than a request. Requests invite negotiation, and the negotiation will be conducted between one person who is proposing an evening off and several people who are agreeing that it sounds like a good idea in principle.
Stated as a fact, it becomes a fixed point that the rest of the arrangement is planned around, which is what it needs to be. It also, quietly, makes it easier for everyone else, because a fixed point requires somebody to cover it, and being asked to cover a specific evening is a far more actionable request than being asked to help more.
Expect it to feel wrong at first
The first several times, going will feel like a small dereliction, and you will spend part of the evening thinking about the house. This is not a sign that the arrangement is wrong. It is a sign that it is new, and it fades on a timescale of weeks rather than days, but only if the thing recurs.
This is why one weekly commitment held reliably is worth more than an occasional larger break. The recurring version becomes ordinary, and ordinary is the state in which it stops costing anything to attend.
The long view
Caring arrangements last much longer than anybody plans for at the outset. Almost everything about them is decided in the first months on the assumption of a shorter horizon, including the quiet assumption that the carer's own week can be suspended for the duration.
It can be suspended for a while. It cannot be suspended for the actual length of these arrangements without something giving way, and what gives way is usually the sustainability of the whole thing. Protecting an evening is not a concession to the carer at the expense of the arrangement. It is one of the few things that makes a long arrangement possible.