Looking for a story where there are four people who think they are on a spaceship but are actually part of a isolation/simulation experiment. One of the females writes a short story that is a thinly-veiled version of their life, in which the spelling of the character's names is slightly altered. There is a love triangle of some sort. The experiment comes to an abrupt end and the participants are shocked when the doors open and there is no space beyond . . .
This is Something Strange by Kingsley Amis. The anthology that I remember it from is Possible Tomorrows published in 1972 and reprinted in 1973, but as you mentioned in your comment, it was also in horror anthologies - The 2nd Fontana Book of Great Horror Stories and The Lucifer Society: Macabre Tales by Great Modern Writers.
I misremembered the name of Bruno's analogue in the story within a story that I mentioned in my comment - it was Norbu, not Bornu. The other characters in the "spaceship" were named Myri (the writer of the story within the story), Lia, and Clovis.
Another plot detail that I remember is that the final psychological test imposed by the experimenters was the reveal that the spaceship occupied by the four characters was the only one that experienced the "strange events" after maintaining the belief that this had happened to many other spaceships.