Kurt Busiek's Astro City

A man named Michael Tenicek keeps dreaming about a woman he never met it is causing him to resort to drugs to not dream of her.

The Hanged man tells him that there was a battle with a time-traveling supervillian named Time Keeper that broke the time continuum and reality, that the heroes fought and won, but there has been some changes after the reconstruction of reality, and this woman was his wife in the precedent version of reality because her grandparents never met. The Hanged man offers to erase theese dreams but Michael decdes to keep the dream so he can still remember her even though he never really knew her.

#06 on Wizard Magazine's "100 Best Single Issue Comics Since You Were Born" list.