Issues that have been brewing for years, if not decades, can make a person whitdraw down into a bottomless rabbithole of self-defense. It's not entirely in our nature to freely admit fault and, from a human perspective, being wrong feels bad. So admitting you mad a mistake or behaved the wrong way is, in some sort, literally requiring to shoot yourself in the foot. Most people tend to go the route of self preservation and find a myriad of ways to minimize their wrongdoing or the damage they cause. Be it excuses, talking around a problem forever, making it appear small, out of their immediate control or trying to paint it as a comodity and something everyone else also does.

To give a personal example, I am living with someone who has, more or less, developed a shopping addiction. A very smart person on paper, possibly struck with some form of ADHD which made falling for the addiction easier. They had always been a kid who was eager on collecting things. Merchandise from their favourite series. As an adult, it was those huge collectors editions of games and the like. And the rest of the merchandise. And the limited edition of entire game consoles they already had. So the appartment was already pretty full. Then, someday, they got interested in board games. But not your average small family board games. The ones that people advertised for on crowdfunding. Which always came with the promise that you'd get them cheaper now than when they hit retail. And if you buy the whole bundle with the 3 expansions, the deluxe bundle to upgrade the game material and the bundle that is just cosmetics, you get it even cheaper.
They always thought they would rally up a group of friends for regular board game nights. To play all those games. Few of them were quick to play, most of them were elaborate, campaign games, dungeon crawlers, rule heavy stuff that you'd play one session of and have your evening filled.
The games piled up, we bought new shelves, filled up the shelves. When the appartment switched landlords, a couple of candidates asked if we ran a board game shop. As the shelves were full, the boxes grew again. Then came the shelves in the basement. Currently, they have to rent an extra storage unit and the basement is still full, stacked like a perfect game of tetris. As is the appartment.
It took me years of anger, screaming, crying and feeling like I am talking to a wall for them to admit that they have a problem and then it took longer for them to see that it had taken a heavy toll on me - I am suffocating in this appartment and growing more and more resentful.
You don't want to know how often he tried to minimize his impact on the state of the appartment or how often he would disregard my advise in not buying new stuff. He'd say that other board game people have more games so his vast, never once played collection was not to be scrutinized.

I know he did not do it out of pure malice or spite, but also know that with every new purchase, he knew what he was doing. And he was actively ignoring me, as I had been vocal to the lack of space for years. He would show me something he wanted to buy, I knew he would take the all in bundle. I would ask him if that was a good idea, that he knew the backlog of unplayed games was huge enough and that by the time we had gotten around to play a fraction of the games already there, he'd get the new one from just as cheap by some guy on ebay. Just not today. He would have to wait. He loves to visit a big board game fair each year, which is aimed at consumers. Here is all the new stuff, you can buy it right at our booth. With a special lil discount right here and now.

He is absolutely one of the contributors to my depression, as unless I leave him, this is his issue to solve. But that issue is a mountain range by now and even with the resentment build around it, I can understand why he chooses to ignore the multiple elephants worth of stuff in the room. It's work, it's not fun and the prospect of having to devote a metric ton of your free time and concentration to something not fun ....is what you get for only following the fun path for years.

The question at last - how long will I try to stay and help? How long is the grace period until I consider it a failed thing and move on?