You can't force him to get help, as others have said, and it sounds like the way he is treating you is really affecting you. I personally feel he is being manipulative and abusive. His current situation explains this, but doesn't excuse it.

I want to tell you something very, very important. You say: I couldn't forgive myself if the one time I ignored him were the one time he followed through and killed himself. It would not be your fault if he killed himself. Suicide is an individual choice and he is using the threat of it to manipulate you and hold you emotionally prisoner.

The fact that he may be suicidal does not give him the right to treat you in the way that he is, nor does it oblige you to support him, keep in touch with him or help him. It's wonderful that you care, but it sounds like it's having a negative effect on you.

The first step in dealing with this is to recognise that, if he does commit suicide, it will not be your fault. You are not responsible for his feelings or his actions.

Secondly, I think you need to stop having contact with him and enlist a third party in any discussions about the house. I would strongly advise you give him an ultimatum: he needs to get help and he cannot contact you until he does. You will be sorry if he contacts you and you are unable to reply, but that is his choice, not yours.

I would personally consider getting the police involved and getting him out of your house, as he is behaving in very abusive ways. I'm sorry you're having to deal with this.