A promise only proves something once it gets inconvenient to keep.

Promises kept while convenient tell you nothing, because no promise was needed to produce that behaviour. The proof only turns up when keeping it costs you an evening, a better offer or some comfort, which is exactly why that moment feels like permission to reconsider. The cost is not an obstacle to the promise. The cost is the content of it.

Look through what you have agreed to and find the one that has since turned inconvenient. Keep that one deliberately, and notice the arguments your head starts producing for getting out. If it genuinely cannot be done, say so rather than letting the day arrive.