It may not be the most popular, positive advice you’ve ever heard, but it is reality. In any relationship you can only give what you have, and if you are neglecting your own needs, eventually that will lead to having nothing.
In the case of trying to support someone dealing with depression or healing from trauma, being there all the time, and then crashing out with nothing left to give, is probably doing more harm than good for your friend. Instead of having realistic expectations and modeling a lifestyle that includes self-care, your friend is left wondering why someone they depended on disappeared, again.
There’s some good, honest, advice in the article. I suggest not just reading it, but also talking about it if you have a friend you are supporting. Simple honesty will go a long way.