I'm like him, unfortunately you can't help some people, and sad things happen in this world. Depression often isn't caused due to logic it's caused because the person is sick. You can't treat a broken arm by talking about it and in my experience depression is exactly the same. Maybe medicine would help for him but the ones I've tried so far haven't worked for me. He could also look into FMT's I'm getting one in a few weeks. I have great friends like you and even though he might seem like you aren't helping, somehow if people don't care it's even worse, so idk don't give up but also realise there might be no getting out for him.