There was a sanctioned-suicide forum on the darknet a while ago. It was a small community, they barely had any activity but it was a thing back in 2015. And then vice wrote an article about that forum - it's the one I linked - and it caused a severe influx in activity. Many new members joined and a lot of them were trolls, which basically caused the forum to dissapear. 4 years later, we have a clearnet version of said website. But apparently - that's what I got from the Admin, this site isn't connected to the darknet-website at all. It just happened to have the same name.
https://www.vice.com/en_us/article/nze5ww/the-deep-web-suicide-site
I don't know of any helpful websites that are about suicide. I just know markets.