I had a bone marrow transplant as a teenager, currently 26 years post op. Those days, BMTs were still very early research. Mortality was 90%.
My primary oncologist at the time told me: People are not statistics.
Your first job as friend, patient advocate, care giver, or whatever other role you wish, is to leave your issues at the door. Your friend needs all their energy towards staying alive. They don't need anyone else's problems, issues, negativity, doubts, whatever.
Your second job is to not take away hope. No matter what the situation. It's the doctor's job to deliver the bad news. Your job is to suspend disbelief and always be supportive.
After my treatment, I volunteered for many years, visiting patients, helping out, etc. I've also had patients live with me while they're in town for treatment. Nothing as extreme or taxing as hospice care, but also not a cake walk. And I don't volunteer when my head's not straight, knowing I'm not able to do the two jobs above.
Lastly, sometimes your job is to help the family, more than the patient. Sometimes the patient has accepted their fate, is in a ICU/coma/whatever, and they're doing fine mentally and emotionally whereas the family now has to struggle with their grief.
Best wishes. You're a good friend to your neighbor.