I ended a long-term friendship last year. I supported my friend through many hospital admissions for depression (visited her a lot even though it was over an hour's ride on the train and half an hour's walk).
But when she decided she wanted to be anorexic (yes, she really did put it that way) I didn't understand why. I am dealing with weight gain the proper way I know how - with healthy food and 45 minutes of exercise every day. My friend kept sending me texts about how she threw up her dinner every night and how she felt guilty about eating any food, how she was tired all the time and yet how pleased she was at losing weight and asking me how much I weigh, which is many more kilos than she does. Eventually I said to her that I couldn't support her down the path she chose for herself and the stuff she sent to me was very triggery and I couldn't handle it. She said I was giving her an ultimatum - my friendship or anorexia. And she wouldn't choose me. So our friendship ended.
I still think about her a lot and hope she is well and recovered.