In William Faulkner's short story "A Rose for Emily", the room upstairs her old, decayed mansion is one of the enigmas that the townsfolk, as a combined narrator, confess to want to discover. 

Already we knew that there was one room in that region above stairs which no one had seen in forty years, and which would have to be forced. They waited until Miss Emily was decently in the ground before they opened it.

The room had not been seen in forty years. We know that many things had been mentioned by the townsfolk narrator which confirm that there have been strange dynamics going on in the Grierson house.

First, we learn that, years before, the very strange and reclusive Miss Emily had begun a relationship with a Northerner. This was shocking to everyone, but they had the best interest of such a strange person in mind. After sometime, the courtship seems to change for something more serious. 

We learned that Miss Emily had been to the jeweler's and ordered a man's toilet set in silver, with the letters H. B. on each piece. Two days later we learned that she had bought a complete outfit of men's clothing, including a nightshirt, and we said, "They are married." We were really glad. [...].

Then, we learn that Homer leaves for a brief period of time. He returns after three days, according to witnesses. However, that is the last they ever see of Homer ever again. Emily is seen only sporadically, and her servant is also barely seen. This is the beginning of Emily's reclusive period. 

It is then when we get to the last part of the story and "the room upstairs" that had not been seen for forty years is finally opened. What they see shocks them:

A thin, acrid pall as of the tomb seemed to lie everywhere upon this room decked and furnished as for a bridal: upon the valance curtains of faded rose color, upon the rose-shaded lights, upon the dressing table, upon the delicate array of crystal and the man's toilet things backed with tarnished silver, silver so tarnished that the monogram was obscured.

This is the dead giveaway: Emily had intended to turn that upstairs room into her bridal suite. Remember how the objects in the room are the very things that she buys in town when the people determined that she and Homer were finally married.

However, it seems that Homer had intended to leave Emily, originally, for good. This happens during that time when they first see him leave town. Somehow, Emily lures him back and, three days later, he is seen for the last time entering the home. This tells us that Emily poisons Homer with the rat poison that she is seen buying at the chemist sometime after Homer had pronounced his preference for men and his dislike for marriage at the Elk's club. By poisoning Homer, Emily gets to keep him forever...in the bedroom suite intended to be their marital bed. 

The man himself lay in the bed.

For a long while we just stood there, looking down at the profound and fleshless grin. [...] What was left of him, rotted beneath what was left of the nightshirt, had become inextricable from the bed in which he lay....

Then we noticed that in the second pillow was the indentation of a head. One of us lifted something from it, and leaning forward, that faint and invisible dust dry and acrid in the nostrils, we saw a long strand of iron-gray hair.

This shows that Emily lived and slept with Homer's body for over 40 years in that room upstairs.