Sorry you are in this predicament, it surely can't be easy.
I agree with DontRemember and Bekind, he needs professional help for sure and I would take him to the ER. If you absolutely feel you can't do that tonight, I wouldn't leave him there on his own and would try to get him to the ER as soon as you are able.
No, this is not your responsibility but at this stage he does need that help and leaving him there could be dangerous.
How you deal with this going forward is a different matter. Please keep us updated with how you get on.