You are reading a short story and you reach a point in the story where the characters return to their normal lives and the tension in the story decreases which plot element does this part of the stort represent

The five stages of action are: exposition, rising action, climax, falling action, resolution. When the tension  in the story decreases it is called resolution.

If while reading a short-story you reach a point in the story where the characters return to their normal lives and the tension in the story decreases, this part most likely represents the resolution element of the plot.

Explanation:

In a literary work such as a short-story or a novel, a play or even a film, the plot or story-line is the sequence of events in which each event affects the next one in what it is called the cause-effect chain. Many of these plots follow a specific structure of different elements needed to constitute a story. It starts with the exposition, then the rising action, the climax, the falling action, and lastly the resolution. In the resolution, the characters of the story most likely return to how their lives were before the rising action started to affect their lives, and the tension previously present has now decreased or disappeared.

in june, we will have been married for eighteen months. (i am assuming this is what you want? the sentence, as you have presented it, is grammatically incorrect--   you want it corrected, yes? )