What was the thing that ruined a friendship?

She had some serious health issues and just refused to get help or even acknowledge it.

It started with her being quickly out of breath and not wanting to go outside anymore. Even going shopping together slowly became impossible. At first she'd ask to sit down a lot, like every half hour. We were in our mid 20s, so that was already a little concerning. Eventually she'd just say she didn't want to go out at all, because it seemed too much for her. Over the course of 2 years it became so bad that she even refused to walk 20 minutes from her place to the cinema because she was too tired. And no she was not overweight, she always looked like her weight was in the normal range.

Of course I tried to talk to her. I carefully tried to point out that being so exhausted all the time and not being able to walk 30 minutes without needing a rest wasn't normal at her age. But her answer was always "That's just me, I'm just like that."

One day after three years of her condition slowly getting worse she slept over at my place. In the evening she made herself a sandwich and put it next to the couch where she slept. I asked her why and she explained that she needed to eat something right after getting up before she could even do so much as sit up in bed. Otherwise she'd feel dizzy. She also told me that she regularly faints when getting out of bed. Like, she'd stand up and wake up on the floor several minutes later. I way so alarmed. I begged and pleaded with her to see a doctor. I told her having to eat in bed while lying down because otherwise you black out when sitting up is not normal. We had a huge fight. She insisted that "that's just who she is", not a medical condition but her being a little quirky. She drove home angrily and we never talked again.

I did worry for her a lot. But in the end you can't make someone care for their health if they absolutely refuse to. Watching someone you care about deteriorate and being unable to convince them to care for themselves is very painful. Oh and before you think this was a money issue: we live in Germany, going to the doctor wouldn't have cost her a dime.