“No story ends happily. The happy ending is only about knowing where to end on a smile, at the very moment where fortune is still on the ascent. The open road. The wedding." Sunnyside by Glen David Gold, as quoted in Sunnyside II – Count no man lucky until he is dead — Crooked Timber.
Happiness is all about the editing. Things happen around us, we make up our own stories. If we're smart, we pick the happy moments to declare a chapter done, signed, sealed for ever. It can't be undone, the unchanging past is more eternal than the universe.
Some chapters are long, some short. The last chapter ends badly, but it's only one among many.