Supporting others is hard.
Sometimes you will offer everything you can, and your friend won't get better (at least, not yet.) That's not your fault.
You did what you could. You are not responsible for what is outside of your control.
So focus on what you can control. Accept. Encourage. Hug.
Speak truth and magic words when the time is right but mainly, listen.
Trust your friend to be stronger than they know. Give time the opportunity to heal. Believe that things will get better, and help your friend to believe it too.
One day, things will be better. For now, do what you can.
It will be enough.