Hey there. Thanks for posting. I hope I can be of some help.
It's quite difficult to explain depression and suicidal ideation to someone who has never really experienced those things. I find, many times, people try to combat depression with positivity and hope-centric approaches. Sadly, this often does not work, and in fact can make the depressed person feel even worse because happiness is something they can't achieve. There's a chemical reason why they can't, but they feel like it's a moral failing, and it only serves as ammunition to hate themselves further.
I'm in a good place now, but I have dealt with more than my fair share of depression, and several suicide attempts. Depression in its very essence is separation and isolation. It prevents you from connecting. At least that is how it was for me. The thing that helped most from loved ones was when they came down to my level and sat with me in the darkness. That doesn't mean they let me get wrapped up in the story of why I was feeling the way I was feeling, and they didn't give permission for self-harm or suicidal behaviors, but they were just there, sitting in the dark. And that brought a little light, because someone got it. They weren't trying to drag me up; they were letting me know I was okay as I was. And that really helped.
You can also always ask your friend if they need support, or advice, or anything else. Be prepared they'll probably say they don't know what they want or need, so again, just be in their corner supporting them quietly and let them know you're there for them.
Hope this helps.
PM me if you need anything.