Ok I read this around 4 years ago.
It's a short story

The story is about a "Neet" who is overweight and is a smoker. He gets trapped in an infinite daily loop in his apartment. He finds that he can't leave his apartment and every day whatever food he ate is replaced with the same food from the previous day. Eventually, he gives up on ever escaping his apartment. He spends his days getting in shape and even quits smoking until one day he finally discovers his front door is open and the loop is broken. Instead of leaving, though, he finds that he has gotten so used to his tiny living space that he shuts the door and decides to go back into the loop but, this time he gets stuck in his bathroom and the only thing he can eat every day is the water in the toilet. The ending is him starving to death alone in his tiny bathroom.

That's one of the stories from Friday: Forbidden Tales, if memory serves. I'll check which one and let you know.

Edit: Okay, found it - the first 3 chapters; title: The Room.