someone is going to die if I don’t do anything before August 23rd

I came across this comment on tiktok in which a guy was talking about August being his last month. He was basically saying that he’s tried everything and that there’s really nothing left to live for, that there was no point. I reached out really hoping to talk him out of it but he flat out told me before we even got to a proper discussion that if those were my intentions that he didn’t want to waste my time by being a burden. I told him I wanted to listen to him, otherwise I wouldn’t have texted him. He’s about the same age as me (17) and lives in the UK. He doesn’t wanna tell me his name but he told me what his plan was. Treat himself to nice food and go to the arcade (basically try to enjoy life one last time as a gift to himself) and then jump in a pier/river at around 3 am and let himself drown and be washed away. He said it was perfect cause he wouldn’t be found before months and by then his body would be unidentifiable. He will leave no notes. He specified doing it on the 23rd because he always felt connected to that number and said that it fell on a Sunday which meant “a new beginning”. I live in Canada so I don’t really know what to do. I am already involved with him by now so the only bad thing that could happen is him dying and me doing nothing to stop it. He did also mention that it started getting really bad in October as he started abusing substances and alcohol. He overdosed and woke up feeling deeply ashamed (like he’s burdening his family). He doesn’t even get up to pee so he just pees himself. I don’t really know what to do.