If you are really worried he will do something to himself, call 911 and explain the situation to them. Did he say he was going to hurt himself or has he threatened to in the past?
He is a grown man and you are not responsible for him.
My ex told me he was going to kill himself when I broke up with him. I thought that I had to stay there for him. I didn't know then that this is a manipulation tactic and my poor ex wasn't the first to use it. It is really an awful, awful thing to threaten just to control another person. It wasn't until reading a post on here about it that I started to understand how I'd been duped.
Most people if they really want to hurt themselves will just DO IT and not talk about it. If they want to control and manipulate you, they will claim they are going to do it. That said, suicide threats should always be taken seriously.
If you have a real concern, 911 can send somebody to check on him. They are trained and equipped to provide help if he's really needs it. If he's BSing, he will be quick enough to tell them there is no problem.
I wish I had known to call 911 for my ex rather than being dragged into his awful manipulation tactics.