And this is why you have people committed to hospitals. I know a lot about mental illness and those institutions that help people. These institutions are the only thing that can save these people because they can't or won't save themselves. Usually these situations end in suicide.
You can lock him in a mental institution. But things will never be same again between you:
If he believes you care about him, want the best for him, then you do that, you will have lost his trust.