It's one of the older stories on this site. A one-shot story, probably anywhere after 2008.
(?)Story starts with doctor talking to the Son, telling him his mother has amnesia due to a car accident(?). They shortly end up finding at the hospital that she has lost several years of her memory and doesn't believe she has a Son and thinks that he is joking(?) and is more likely her boyfriend/husband. Her mental age regression make her uncomfortable with reality and stresses her and the doctor pulls the Son aside.
The doctor advises him to not stress her and act as the husband/boyfriend that she thinks he is so he doesn't stress her.
They eventually consummate the fake relationship and she ends up remembering midway-through when they are sleeping together but continues with the relationship.
(?)Story starts with doctor talking to the Son, telling him his mother has amnesia due to a car accident(?). They shortly end up finding at the hospital that she has lost several years of her memory and doesn't believe she has a Son and thinks that he is joking(?) and is more likely her boyfriend/husband. Her mental age regression make her uncomfortable with reality and stresses her and the doctor pulls the Son aside.
The doctor advises him to not stress her and act as the husband/boyfriend that she thinks he is so he doesn't stress her.
They eventually consummate the fake relationship and she ends up remembering midway-through when they are sleeping together but continues with the relationship.