etb, I spent 10 years with the knowledge that my grandfather would commit suicide. Mind you, he was 94 when he finally committed the deed. Still, it was quite a traumatic process. I suppose I could relate it to dealing with a love one who you know has a terminal illness that is not necessarily immediate. You KNOW they are going to die and you just have to keep living life knowing that there really is nothing you can do to prevent the death. Just like old age, death is guaranteed.
Does that help you? Maybe not, but that is the reality of it. Your H could get into a car and have a fatal accident. You may always wonder if it was "accidental" or suicide. You may never have that answer. Some questions just cannot be answered.
Take a look at ninelives' W. There was nothing he could have done to prevent her suicide. He could be there to support her when she asked for support, but it was a daemon that she lived with (bi-polar) in the same way that your H will live with his depression.
You have suspicions about your H's potential act. Do what ever you can do to not worry about something that may NOT happen. Like any friend, you can support him when he needs support. If he (directly) asks for support to deal with his issues, direct him to professionals that are equipped to help him.
In the mean time, all you can do is enjoy the moments that you do have with him. It is all you have.
