Efforts to avoid covid can feel futile when living in close quarters with a sick person, but it IS possible to escape infection! Here is the story of a person who stayed healthy and continued testing negative while sharing space with a sick person. I'll refer to the healthy person as H and the sick person as S.
H and S live in a small apartment. The living space is divided into two rooms that are connected by a large opening. There's also a small bathroom without a window.
H and S spent more time together than was ideal. Whenever together, H wore an N95 mask and also kept the window open.
Although H and S slept in separate rooms, the opening between the rooms meant that this wasn't enough to keep H safe. H was aware that some people sleep wearing N95 masks, and tried to do that. However, H couldn't manage it. After a sleepless night, they took their pillow over to the window, opened the window all the way, and slept directly under the open window. They slept there for the next 10 nights.
Tooth brushing was done at the same open window, spitting into a cup instead of a sink.
There was no completely safe way to shower. H did the best they could by starting each shower wearing an N95 mask and washing from the neck down, removing their mask and washing their head only after everything else was clean. Then, they put the N95 back on immediately, without even drying first.
Food was a challenge. Much of it was eaten in an unsafe environment, chewed and swallowed hastily so that the N95 could go back on. H's greatest regret about preparedness was not having any MREs available that could have been consumed next to the open window in their room.
It took days for S to get an appointment with their doctor. Meanwhile, they attempted to lower their viral load by following some of @ducky's advice: https://covidbc.webfoot.com/what-to-do-if-you-get-covid-19/
I hope that this case history will be helpful to someone in H's position. Covid CAN be avoided!